ASHCROFT STEAM INDICATOR IN BEAUTIFULLYCONSTRUCTED BOX WITH STAINESS STEEL, PRE-WORLD WAR I LOCKS AND HANDLE.

INCLUDES PERIOD PRECISION RULERS AND NOTEPAPER SEE IMAGES…

USED BUT INPRISTINECONDITION~!

THIS IS AN CLASSY ANTIQUE, NO DOUBT!

I have had this indicator for at least 27years.

It was my Great Grandfather’s. He was a Navy Man.

When I asked him for it, he wanted to know why I wanted it... back then I only wanted it because I thought it was the coolest thing I have ever seen... I still do think that but know that there must be someone who would like to have this on display. If so, Enjoy!

I took this cool antique to the AntiquesRoadshow this past August 2014. I was told that if I sold this that I should, at the very least, ask for $850.00 due to condition and the box.

What is an indicator?

This information wasgathered from another site… it is merely to give you info on what the springindicator/calibration tool was used for… If by any means you have betterinformation, please feel free to share it with me. If you read the directions that are on the toplid of the box, to this tool, it also is loaded with information!

Thank you!

THE Perfected Ashcroft-made Tabor...

An indicator is a small, originally mechanically-operatedinstrument that gives an insight into the operation of a range ofpressure-operated machines — steam engines, gas and oil engines, compressors,condensers, even guns — by comparing the rise and fall of pressure during theoperating cycle. The use of an oscillating drum allows variations in pressureto be recorded on both the outward stroke and the return journey. Exceptingsome of the continuously-recording instruments and virtually all maximum-pressurerecorders, indicators usually give a trace in the form of a closed loop.

A steam engine works by allowing steam to entera cylinder behind a piston, then pushing the piston along to the opposite (far)end of the cylinder. The piston is connected to a crank, and the crank is oftenconnected to a heavy flywheel. If the engine is single acting, the steam wouldbe exhausted at the end of the piston stroke and the momentum of the flywheel,once the engine was running, would return the piston passively to its originalposition. Steam would be introduced, and the cycle would recommence. Mostengines are double-acting, however. When the steam is exhausted from the headside of the piston at the end of the outward stroke, another charge of steam isintroduced on the crank side of the piston to actively push the piston backagain. This results in continual motion as steam is admitted and exhausted onboth sides of the piston alternately.

The engine indicator is a fascinating instrument that records howthe pressures in the cylinders of steam and internal-combustion engines changeduring the operating cycle. Used properly, they can identify problems rangingfrom bad valve settings to constricted steam pipes.

One of the major catalysts in development was the increasing realizationthat the steam engine, useful tool though it had proved to be, was inefficient.Many reasons have been advanced to account for this process, but it is probablethat — once the Watt-type engine began to replace the old Newcomen\'atmospheric\' designs — it could be seen that too much coal was being consumedin relation to output.The first attempts to register pressure generatedin the cylinders of steam engines were undertaken with columns of mercury, thelevels being judged by the displacement of the metal in small-bore tubes.

ABOVE
The advent of the Watt-type steam engine inspired the pursuit of efficiency.The first indicators required careful watching, as the readings could only betaken manually, but it was not long before the automated moving-tabletinstrument had appeared.

This method was unsatisfactory, as the mercury often oscillatedtoo greatly for satisfactory recordings to be taken and the glass tubes wereprone to break. A better solution was proposed by James Watt (1736-1819), whois customarily accorded credit for defining the \'horse power\' and was also thefirst (as far as we know) to produce a \'stand alone\' method of indicating steampressure within a cylinder. About 1790, Watt produced an indicator in which asmall piston, travelling within a brass cylinder, moved a pointer; the greaterthe pressure, the greater the deflection, which, as the engines of the day wereslow running, could be seen by an observer. A skilled man could note theprogress of the pressure during the steam phase and also the vacuum produced bythe condenser.

The first major improvement in the design of the Watt Indicator was madeby an employee of Boulton & Watt, John Southern (1758-1815), who designedthe first method of recording the operating cycle of the steam engineautomatically. In the summer of 1796, Southern suggested adapting the\'recording indicator\' by adding a recording-board or tablet that slid within asupporting frame. A cord attached to the beam pulled the tablet sideways as, simultaneously;the pencil-pointer recorded the rise of pressure in the cylinder on a sheet ofpaper. As the beam returned, a weight attached to the free end of the operatingcord reversed the movement of the tablet. The pencil recorded the cylinderpressure as it dropped to nothing, and in so doing closed the diagram ofpressure against time.

The shape of this diagram remained characteristic of indicatorsmade into the present century, the earliest datable survivor being made inJanuary 1803. However, indicators were in perpetually short supply until the1820s. This was partly becauseJames Watt was a secretive man, obsessedwith keeping his ideas from others, and the development of a recordingindicator was kept from prying eyes. However, details of one such instrumentwere published in an \'Account of a Steam Engine Indicator\', a letter submittedby \'H.H. junr.\' toThe Quarterly Journal of Sciencein 1822.This credits knowledge of the indicator to Joshua Field of Maudslay, Son &Field, and manufacture to a foundry owned by \'Mr Hutton of Anderston\',Glasgow.Indicators of this type were made into the 1840s, and the idea ofa moving tablet reappeared several times in the late nineteenth century. Theculmination was a Wayne design, patented in Britain in 1894.

The first major advance to be made after the reciprocating tabletwas the oscillating drum. The credit for this is customarily given to theScotsman John McNaught—largely on his own testimony!—but circumstantialevidence suggests that the idea may have occurred first to Henry Maudslay. Theoriginal McNaught indicator had the recording drum concentric with the pistoncylinder, but the perfected version had the drum on a platform that protrudedfrom the cylinder laterally. A swiveling pulley, known as the fairlead, allowedthe cord attached to a suitable part of the engine to approach the indicator atan angle.

The McNaught indicator relied on a comparatively steam-tightpiston sliding in a tube beneath a large coil spring. When the outward strokeof the engine piston began, the pull on the cord turned the drum through ahalf-revolution. The admission of steam to the cylinder raised the pencil tomake its trace. When the inward stroke of the piston began, a helical spring inthe recording drum rotated it back through the half-circle to its startingposition. This allowed the pencil to complete its loop.

The McNaught indicator was popular, as it was comparativelysimple, easily copied, and acceptable efficient. Many attempts were made toimprove it, notably by Duvergier in France and Joseph Hopkinson in England, butmany of these experiments sought methods of obtaining continuous diagramsinstead of improvements to the basic instrument. From this period, too, camethe first attempts to develop the so-called \'lining indicator\', whichconstructed an average diagram from a large number of strips taken fromsuccessive engine cycles, and the first integrating \'totalisers\', which deducedthe cumulative or average values numerically.

Once the value of the perfected McNaught rotating-drum pattern hadbeen universally admitted, steam-engine indicators were made in great quantityby many manufacturers. But they were expensive. Regarded as precision tools,they still cost more than four times the average English weekly wage in 1914.

The next great advance was made in the USA, where the firsthigh-speed steam engines had been developed in the 1850s. The advent of theAllen engine, promoted enthusiastically by Charles Talbot Porter (1824–1910),was the catalyst. Porter realized that the McNaught-type indicators being madeby the Novelty Iron Works were too prone to vibrate when used at high speed,giving tremulous diagrams that were impossible to interpret, and soughtsomething better. The project was given to consulting engineer Charles B.Richards (1833–1919), who within a very short time had produced a workabledesign by combining the offset recording drum and the internal coil spring ofthe McNaught with a system of levers, inspired by Watt parallel motion thatamplified the movement of the piston four-fold. This kept the movement of thepiston to a minimum, allowed a short stiff spring to be used to dampvibrations, and kept the instrument as compact as possible.

The Porter-Allen engine and the prototype Richards indicator (madeby the Novelty Iron Works) were exhibited at the International Exhibition inLondon in 1862. There the engine attracted much adverse comment, but proved towork smoothly and in perfect safety-confounding the doom-laden predictions ofits many detractors. The indicator was used successfully to test a variety ofengines on display, though one or two well-known British engineers refused tohave anything to do with it. A trial of a railway locomotive was arranged, andthe existence of the indicator came to the attention of Elliott Brothers,renowned as makers of optical equipment. A license was negotiated, and thefirst Elliott-Richards indicators appeared in 1863. More than ten thousand ofthem had been made by 1876, and work continued until the end of the nineteenthcentury.

The Richards indicator proved to be sturdy and reliable, and wasstill being used in quantity when Europe went to war in 1914. However, thesuccess of the Porter-Allen engine had begun a quest for ever-greater pressuresand ever-increasing speed. Above 250 rpm, even the Richards indicator struggledto provide reliable diagrams. This was largely due to the inertia of the partsin the amplifying mechanism, which were long and comparatively heavy.

The first real successor was the work of the American engineer,Joseph W. Thompson, whose indicator was patented with the backing of theBuckeye Engine Company in 1875. The Thompson amplifier (which embodied a moremathematically correct straight-line approximation than its predecessor) wasmuch lighter than the Richards equivalent, taking the form of the letter \'M\',and soon proved to give good diagrams at 350 rpm or more. Consequently, Thompson-typeindicators were made by many companies after Buckeye withdrew. The best knownare the American Steam Gauge Company, Schaeffer & Budenberg, JamesRobertson & Sons and Dobbie McInnes. Dobbie-patent instruments were stillbeing made in the 1960s substantially in their original 1898-typeexternal-spring form.

ABOVE
The three principal U.S.-made indicators of the late nineteenth century: anearly American Steam Gauge-made Thompson (left), the perfected Ashcroft-madeTabor (centre), and an 1895-type Crosby (right).Bruce Babcock andMuseum of Making collections.

The indicator designed by Harris Tabor, patented in the USA in1878, offered an alternative to the Richards and Thompson patterns. Made by theAshcroft Manufacturing Company from the early 1880s, the Tabor relied on aslotted vertical standard to direct the pointer in a straight line. Theearliest Tabor was too weak to succeed, but the modified design of 1886 provedto be amply strong enough to compete on level terms with the Thompsons.

When the Thompson patent lapsed, many other designers tried theirhand. This is particularly evident in the USA, where instruments such as theStraight Line (1890), the Calkins (1890) and the Lippincott (1900) all brieflyprospered. There was even a place for aberrant designs such as the BritishKenyon of 1878 and its US equivalent, the Rae, which used Bourdon-type pressuretubes instead of piston springs; the 1887-patent Bachelder, with its adjustableleaf spring placed horizontally; and the British Simplex of 1894, brieflypromoted by Elliott Brothers, which had a tong-like spring.

If the Thompson system was the most popular prior to 1910, then itwas eclipsed by the perfected Crosby indicator thereafter. Made in Boston,Massachusetts, the 1882 Crosby and its strengthened 1895-patent successor weremade in large quantities. They had the merit of exceptionally light amplifyinggear, much lighter than even the Tabor, and a comparative absence of inertiaeffects.

By 1900, the first of the external-spring indicators were beingseen. The earliest is usually acknowledged as the British McKinnell &Buchanan, patented in 1893 on the basis of the Richards mechanism, but theoriginal Maudslay & Field indicator —sometimes said to date as earlyas the1820s — may have taken a broadly comparable form.

Many of the earliest designs were poor compromises, including theexternal-spring Tabor, the first Maihak and the 1902-type Dreyer, Rosenkranz& Droop pattern. The problem was simply that spring-support standards orrods had to be accommodated on the cylinder cap or platform of an otherwiseconventional enclosed-spring design. The ideas made sense financially, but wereless acceptable where efficiency was concerned. The external-spring Tabor,patented in 1900 by William Houghtaling, even had the amplifying rod spindle ina separate chamber.

The \'second generation\' of external-spring designs had the springsbeneath the platform, above an abbreviated piston cylinder, and were also oftenfitted with vulcanite or similar sheathing to allow springs to be changed whenthe metalwork was hot. The most successful of these indicators were patented byJohn Dobbie in Britain and by William Trill in the USA.

ABOVE
Typical external-spring indicators: a British Dobbie McInnes Design No. 1A\'Large\' (left), with the spring exposed beneath the platform; an AmericanDavidson-patent Crosby (Centre), with the spring above the bridge; and apost-1918 German Lehmann & Michels instrument (right), with the springabove a Crosby-like amplifying mechanism hiiden within a protectivecasing.John Walter and Museum of Making collections.

\'Third generation\' external spring indicators returned to springsthat were mounted on top of the platform, but often relied on extended pistonrods or bifurcated or duplicated amplifying links of Thompson or Crosby type toallow the spring to be concentric with the piston rod. Indicators of this typewere made in the U.S.A. in Boston, Massachusetts, by the Star BrassManufacturing Company (Webster patent), the American Steam Gauge Company(Jerrauld patent), and the Crosby Steam Gauge & Valve Company (Davidsonpatent); and in Pittsburgh, Pennsylvania, by the Bacharach IndustrialInstrument Company (Maihak copies). Both Maihak and Lehmann & Michels madeCrosby-type indicators in Hamburg, Germany, in accordance with WilhelmLehmann\'s patent of 1909.

Another idea to see success in the 1920s was the cantilever-springindicator, a descendant of the Bachelder of 1887 patented in Germany in 1924 byAlfred Adolf von Gehlen of Hamburg and made by Maihak AG. This substituted arobust spring-steel bar for the spring, the comparatively minimal deflectionunder load suiting the instrument to high speed/high pressure recording. Theamplifying mechanism and the pointer were essentially the same as the standardMaihaks, however.

Mechanical indicators such as the Maihak Typ 30 and Typ 50 and theDobbie McInnes Design No. 4 were still popular in the 1960s. Though theirdistribution declined as first electric and then electronic analyzers becameavailable, they were regularly used to indicate marine diesel engines. Indeed,the two German manufactures, Lehmag (formerly Lehmann & Michels) andLeutert (successors to Maihak) still offer external-spring and bar-springinstruments for this particular purpose.

Indicatorsand internal combustion

The gas engine patented in France in January 1860 byJean-Joseph-Étienne Lenoir, the first of its type to be exploited commercially(though the underlying ideas had originated in the eighteenth century), finallyprovided the steam engine with an effectual rival. Lenoir\'s engine looked likea small horizontal steam engine, but a mixture of gas and air was drawn intothe cylinder to be ignited at the half-way point. The near-instantaneouscombustion of the charge then thrust the piston to the limit of its travel.Aided by the energy stored in a large flywheel, the motion was then reversed.As the piston returned, a charge was drawn in behind it and fired again. Theprocess was continuous, with two power strokes for each revolution of thecrank.

Several hundred Lenoir engines had been made by 1865, thoughexperience had shown them to be prone to overheat and run erratically if thecylinder-wall temperature rose to a point where the charge was ignitedprematurely. The overall efficiency was merely four per cent: twice as good asthe best steam engine of the day, but still a notably poor return. The Lenoirwas doomed to be the plaything of the rich and the few businessmen who sawpromise in its technology, yet it was also the catalyst for the development of betterdesigns. These included the odd-looking Otto & Langen gas engine of 1867,with a vertical cylinder and a rack-and-pinion to convert the reciprocation ofthe piston-fired upward, returned by gravity-into rotary motion. Overallefficiency of fourteen per cent was more than four times that of the Lenoir,and more than 4500 Otto & Langen engines were made in the 1870s and 1880s.Gas-Motoren-Fabrik Deutz had made more than forty thousand of the 1876-typehorizontal-cylinder successors by 1895.

By the publication in 1897 of Frederick Grover\'s bookAPractical Treatise on Modern Gas and Oil Engines, internal combustion wasso well established that \'Acme\', \'Premier\' and \'Simplex\' — among many others —had become household names. The general design had settled on the classicallayout of the horizontal steam engine, with a sturdy bed-frame and a largeflywheel, though cylinders could be set side-by-side, in tandem, or at oppositeends of the bed.

Excepting the vehicle and aero engines, which were almost alwayspetrol, gas engines were favored (at least in Britain) for domestic and lightindustrial applications. Initial reliance on supplies of \'town gas\', drawn frommains piping, was gradually eroded by self-contained \'producer gas\' units after1900. The smallest producer-gas units offered commensurately limited power, butwere cheaper and easier to run than steam plant. Most relied on a mix of airand steam passed through anthracite to produce combustible gas that could befed into the engine cylinder.

ABOVE
Two examples of reducing gear.Left, the Crosby design.Right,a typical European-type reducing wheel, based on a Stanek design of the 1880s.This particular example was sold with a Lehmann & Michels indicator of theearly 1920s, fitted in the same box. The graded exchangeable bushes allow thereducer to be adapted to a range of cylinder strokes. Museum of Makingcollection.

Analyzing pressure/time diagrams was greatly helped by the use ofa polar plan meter, a mathematical instrument patented in Switzerland in 1853by Jacob Amsler. This allowed any area bounded by a single continuous line tobe quickly and accurately computed, and was an ideal, if expensive adjunct tothe engine indicator. A few planimeters were even boxed with indicators andreducing gear. Among the best-known of the pre-1914 designs are the Swiss-madeAmsler and Corradi, which can be found with the names of distributors ormanufacturers such as Elliott Brothers or the Crosby Steam Gauge & ValveCompany. Keuffel & Esser planimeters were popular in the U.S.A., thoughthey were originally made in Germany prior to the First World War; far lesscommon were the distinctive Lippincott, Trill and Willis patterns, and theearlier \'Coffin Averager\'.

ABOVE
Typical external-spring indicators: a British Dobbie McInnes Design No. 1A\'Large\' (left), with the spring exposed beneath the platform; an AmericanDavidson-patent Crosby (Centre), with the spring above the bridge; and apost-1918 German Lehmann & Michels instrument (right), with the springabove a Crosby-like amplifying mechanism hiiden within a protectivecasing.John Walter and Museum of Making collections.

\'Third generation\' external spring indicators returned to springsthat were mounted on top of the platform, but often relied on extended pistonrods or bifurcated or duplicated amplifying links of Thompson or Crosby type toallow the spring to be concentric with the piston rod. Indicators of this typewere made in the U.S.A. in Boston, Massachusetts, by the Star BrassManufacturing Company (Webster patent), the American Steam Gauge Company(Jerrauld patent), and the Crosby Steam Gauge & Valve Company (Davidsonpatent); and in Pittsburgh, Pennsylvania, by the Bacharach IndustrialInstrument Company (Maihak copies). Both Maihak and Lehmann & Michels madeCrosby-type indicators in Hamburg, Germany, in accordance with WilhelmLehmann\'s patent of 1909.

Another idea to see success in the 1920s was the cantilever-springindicator, a descendant of the Bachelder of 1887 patented in Germany in 1924 byAlfred Adolf von Gehlen of Hamburg and made by Maihak AG. This substituted arobust spring-steel bar for the spring, the comparatively minimal deflectionunder load suiting the instrument to high speed/high pressure recording. Theamplifying mechanism and the pointer were essentially the same as the standardMaihaks, however.

Mechanical indicators such as the Maihak Typ 30 and Typ 50 and theDobbie McInnes Design No. 4 were still popular in the 1960s. Though theirdistribution declined as first electric and then electronic analyzers becameavailable, they were regularly used to indicate marine diesel engines. Indeed,the two German manufactures, Lehmag (formerly Lehmann & Michels) andLeutert (successors to Maihak) still offer external-spring and bar-springinstruments for this particular purpose.

Indicatorsand internal combustion

The gas engine patented in France in January 1860 byJean-Joseph-Étienne Lenoir, the first of its type to be exploited commercially(though the underlying ideas had originated in the eighteenth century), finallyprovided the steam engine with an effectual rival. Lenoir\'s engine looked likea small horizontal steam engine, but a mixture of gas and air was drawn intothe cylinder to be ignited at the half-way point. The near-instantaneouscombustion of the charge then thrust the piston to the limit of its travel.Aided by the energy stored in a large flywheel, the motion was then reversed.As the piston returned, a charge was drawn in behind it and fired again. Theprocess was continuous, with two power strokes for each revolution of thecrank.

Several hundred Lenoir engines had been made by 1865, thoughexperience had shown them to be prone to overheat and run erratically if thecylinder-wall temperature rose to a point where the charge was ignitedprematurely. The overall efficiency was merely four per cent: twice as good asthe best steam engine of the day, but still a notably poor return. The Lenoirwas doomed to be the plaything of the rich and the few businessmen who sawpromise in its technology, yet it was also the catalyst for the development of betterdesigns. These included the odd-looking Otto & Langen gas engine of 1867,with a vertical cylinder and a rack-and-pinion to convert the reciprocation ofthe piston-fired upward, returned by gravity-into rotary motion. Overallefficiency of fourteen per cent was more than four times that of the Lenoir,and more than 4500 Otto & Langen engines were made in the 1870s and 1880s.Gas-Motoren-Fabrik Deutz had made more than forty thousand of the 1876-typehorizontal-cylinder successors by 1895.

By the publication in 1897 of Frederick Grover\'s bookAPractical Treatise on Modern Gas and Oil Engines, internal combustion wasso well established that \'Acme\', \'Premier\' and \'Simplex\' — among many others —had become household names. The general design had settled on the classicallayout of the horizontal steam engine, with a sturdy bed-frame and a largeflywheel, though cylinders could be set side-by-side, in tandem, or at oppositeends of the bed.

Excepting the vehicle and aero engines, which were almost alwayspetrol, gas engines were favored (at least in Britain) for domestic and lightindustrial applications. Initial reliance on supplies of \'town gas\', drawn frommains piping, was gradually eroded by self-contained \'producer gas\' units after1900. The smallest producer-gas units offered commensurately limited power, butwere cheaper and easier to run than steam plant. Most relied on a mix of airand steam passed through anthracite to produce combustible gas that could befed into the engine cylinder.

ABOVE
Two examples of reducing gear.Left, the Crosby design.Right,a typical European-type reducing wheel, based on a Stanek design of the 1880s.This particular example was sold with a Lehmann & Michels indicator of theearly 1920s, fitted in the same box. The graded exchangeable bushes allow thereducer to be adapted to a range of cylinder strokes. Museum of Makingcollection.

Analyzing pressure/time diagrams was greatly helped by the use ofa polar plan meter, a mathematical instrument patented in Switzerland in 1853by Jacob Amsler. This allowed any area bounded by a single continuous line tobe quickly and accurately computed, and was an ideal, if expensive adjunct tothe engine indicator. A few planimeters were even boxed with indicators andreducing gear. Among the best-known of the pre-1914 designs are the Swiss-madeAmsler and Corradi, which can be found with the names of distributors ormanufacturers such as Elliott Brothers or the Crosby Steam Gauge & ValveCompany. Keuffel & Esser planimeters were popular in the U.S.A., thoughthey were originally made in Germany prior to the First World War; far lesscommon were the distinctive Lippincott, Trill and Willis patterns, and theearlier \'Coffin Averager\'.

ABOVE
Typical external-spring indicators: a British Dobbie McInnes Design No. 1A\'Large\' (left), with the spring exposed beneath the platform; an AmericanDavidson-patent Crosby (Centre), with the spring above the bridge; and apost-1918 German Lehmann & Michels instrument (right), with the springabove a Crosby-like amplifying mechanism hiiden within a protectivecasing.John Walter and Museum of Making collections.

\'Third generation\' external spring indicators returned to springsthat were mounted on top of the platform, but often relied on extended pistonrods or bifurcated or duplicated amplifying links of Thompson or Crosby type toallow the spring to be concentric with the piston rod. Indicators of this typewere made in the U.S.A. in Boston, Massachusetts, by the Star BrassManufacturing Company (Webster patent), the American Steam Gauge Company(Jerrauld patent), and the Crosby Steam Gauge & Valve Company (Davidsonpatent); and in Pittsburgh, Pennsylvania, by the Bacharach IndustrialInstrument Company (Maihak copies). Both Maihak and Lehmann & Michels madeCrosby-type indicators in Hamburg, Germany, in accordance with WilhelmLehmann\'s patent of 1909.

Another idea to see success in the 1920s was the cantilever-springindicator, a descendant of the Bachelder of 1887 patented in Germany in 1924 byAlfred Adolf von Gehlen of Hamburg and made by Maihak AG. This substituted arobust spring-steel bar for the spring, the comparatively minimal deflectionunder load suiting the instrument to high speed/high pressure recording. Theamplifying mechanism and the pointer were essentially the same as the standardMaihaks, however.

Mechanical indicators such as the Maihak Typ 30 and Typ 50 and theDobbie McInnes Design No. 4 were still popular in the 1960s. Though theirdistribution declined as first electric and then electronic analyzers becameavailable, they were regularly used to indicate marine diesel engines. Indeed,the two German manufactures, Lehmag (formerly Lehmann & Michels) andLeutert (successors to Maihak) still offer external-spring and bar-springinstruments for this particular purpose.

Indicatorsand internal combustion

The gas engine patented in France in January 1860 byJean-Joseph-Étienne Lenoir, the first of its type to be exploited commercially(though the underlying ideas had originated in the eighteenth century), finallyprovided the steam engine with an effectual rival. Lenoir\'s engine looked likea small horizontal steam engine, but a mixture of gas and air was drawn intothe cylinder to be ignited at the half-way point. The near-instantaneouscombustion of the charge then thrust the piston to the limit of its travel.Aided by the energy stored in a large flywheel, the motion was then reversed.As the piston returned, a charge was drawn in behind it and fired again. Theprocess was continuous, with two power strokes for each revolution of thecrank.

Several hundred Lenoir engines had been made by 1865, thoughexperience had shown them to be prone to overheat and run erratically if thecylinder-wall temperature rose to a point where the charge was ignitedprematurely. The overall efficiency was merely four per cent: twice as good asthe best steam engine of the day, but still a notably poor return. The Lenoirwas doomed to be the plaything of the rich and the few businessmen who sawpromise in its technology, yet it was also the catalyst for the development of betterdesigns. These included the odd-looking Otto & Langen gas engine of 1867,with a vertical cylinder and a rack-and-pinion to convert the reciprocation ofthe piston-fired upward, returned by gravity-into rotary motion. Overallefficiency of fourteen per cent was more than four times that of the Lenoir,and more than 4500 Otto & Langen engines were made in the 1870s and 1880s.Gas-Motoren-Fabrik Deutz had made more than forty thousand of the 1876-typehorizontal-cylinder successors by 1895.

By the publication in 1897 of Frederick Grover\'s bookAPractical Treatise on Modern Gas and Oil Engines, internal combustion wasso well established that \'Acme\', \'Premier\' and \'Simplex\' — among many others —had become household names. The general design had settled on the classicallayout of the horizontal steam engine, with a sturdy bed-frame and a largeflywheel, though cylinders could be set side-by-side, in tandem, or at oppositeends of the bed.

Excepting the vehicle and aero engines, which were almost alwayspetrol, gas engines were favored (at least in Britain) for domestic and lightindustrial applications. Initial reliance on supplies of \'town gas\', drawn frommains piping, was gradually eroded by self-contained \'producer gas\' units after1900. The smallest producer-gas units offered commensurately limited power, butwere cheaper and easier to run than steam plant. Most relied on a mix of airand steam passed through anthracite to produce combustible gas that could befed into the engine cylinder.

ABOVE
Two examples of reducing gear.Left, the Crosby design.Right,a typical European-type reducing wheel, based on a Stanek design of the 1880s.This particular example was sold with a Lehmann & Michels indicator of theearly 1920s, fitted in the same box. The graded exchangeable bushes allow thereducer to be adapted to a range of cylinder strokes. Museum of Makingcollection.

Analyzing pressure/time diagrams was greatly helped by the use ofa polar plan meter, a mathematical instrument patented in Switzerland in 1853by Jacob Amsler. This allowed any area bounded by a single continuous line tobe quickly and accurately computed, and was an ideal, if expensive adjunct tothe engine indicator. A few planimeters were even boxed with indicators andreducing gear. Among the best-known of the pre-1914 designs are the Swiss-madeAmsler and Corradi, which can be found with the names of distributors ormanufacturers such as Elliott Brothers or the Crosby Steam Gauge & ValveCompany. Keuffel & Esser planimeters were popular in the U.S.A., thoughthey were originally made in Germany prior to the First World War; far lesscommon were the distinctive Lippincott, Trill and Willis patterns, and theearlier \'Coffin Averager\'.

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