260 The Microscope. 



occupied for the complete adjustment was only 25 minutes; and, 

 second, that during the entire operation, the machinery of the shop 

 was running at half speed. 



These and similar observations have led the writer to advocate a 

 more extended use of the microscope in the every-day work of the 

 machine shop. By attaching the microscope firmly to the slide rest 

 of the lathe, the ordinary operation of turning shoulders to a given 

 length, and cylinders to a given diameter can be more expeditiously, 

 more exactly, more ecomically performed than by the usual method. 



It is freely admitted by mechanicians that a decided advance ini 

 mechanical construction would be made by the employment of uni- 

 form measvires of length. This can be easily and profitably accom- 

 plished in any well regulated shop, employing as many as 50 hands,, 

 by delivering fi'om a standard-room any desired unit of length, in 

 the same way as tools are delivered from a tool-room. The expense 

 of a comparator, from which any measui'e of length could be 

 obtained within a limit of time which would not ordinarily exceed 

 one minute, would not be great. If this comparator were placed in 

 charge of a person familiar with its use, and in a convenient loca- 

 tion, any workman could have a Calleper set for him in half the 

 time that would be required in setting it to a scale by the usual 

 method, the precision would be incomparably greater, and absolute 

 uniformity would be secured in every dimension of length employed. 

 The various points to which I have briefly called attention, are to 

 be considered simply as illustrations of the many ways in which the 

 useful service of the microscope may be extended. 



On the address in which I am called upon to make this 

 evening, as President of the American Society of Microscopists, 

 I have selected a single application of the microscope in scientific 

 research. I beg to call your attention to the microscope as a factor 

 in the establishment of a constant of nature. 



If a bar of metal which has the faces of each end parallel and 

 at right angles to its axis, is submerged in melting ice, the perpen- 

 dicular distance between the two faces may be said to represent a 

 definite unit of length at the temperature of 82° F or of ^ C. If 

 this distance is identical in length under similar conditions with a 

 certain bar of platinum now deposited at the International Bureau 

 of weights and measures at Bretenie, near Paris, and designated the 

 " Metre des Archins,'' the length of the bar said to be one metre. If 

 now the bar is submerged in a liquid which has throughout its entire 



