THE old adage that time is money was never truer than it is to-day, when results have to be foreseen and approximated to, often under circumstances which give but little opportunity for detailed calculation. In the engineering profession especially estimates for work are frequently required at a few hours’ notice, the importance of being able to make calculations for power, speed, consumption, &c., with rapidity and precision cannot be over-estimated; hence we find advanced engineers making extensive use of mechanical calculators, such as slide rules, planimeters, &c. Of course the slide rule is a very old instrument, but it was more usually regarded as a mathematical toy. Of late years it has, however, for reasons mentioned above, occupied a position of great importance in the drawing office. Mr. Pickworth has perhaps done as much as anyone in popularizing the use of this instrument, as he has made it a subject of special study, and in the manual before us, which, by the way, is in its fifth edition, he describes the principle and the uses of the slide rule in plain and simple language, so that any intelligent engineer’s apprentice need experience no difficulty in acquiring the knowledge necessary to use this beautiful instrument. Mr. Pickworth’s work mainly deals with that form of slide rule known as the Gravét or Mannheim. He shows how to perform so many calculations required every day in an engineer’s office that one is tempted to ask what this instrument cannot do. Of course, in the hands of a loving enthusiast such as the author, the slide rule can be used for all purposes of calculation, but the ordinary engineer will probably use it for a few special purposes, such as calculating circumferences and areas of circles, arithmetic, and perhaps logs. To use the slide rule to its utmost capacity requires considerable preliminary study, hut once its working is mastered the instrument exercises a fascination of its own, and henceforth it becomes a pocket companion to be used in all but the most simple calculations. Mr. Pickworth describes also some other forms of calculators, including the “Boucher," which we ourselves use. In conclusion we would strongly urge young engineers to master the slide rule, and they cannot find a better work on the subject than the one before us. – The Auto: The Motorist's Pictorial, Vol. 3
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