1036 SUMMARY OF CURRENT RESEARCHES RELATING TO 



formed an invariable plane of reference. The Microscope was securely- 

 attached to the platen and adjusted for sharp focus upon the surface of the 

 mercury at one end. The platen was then moved along until the Micro- 

 scope occupied a position near the other end of the groove. This end was 

 then adjusted by elevation or depression as required, until the surface of 

 the mercury was sharply in focus. After two trials it was found that the 

 surface of the mercury was at the same constant focal distance from the 

 Microscope as indicated by the sharpness of definition. Notwithstanding 

 the fact that extreme care had been taken in the original adjustment by the 

 aid of the spirit-level, it was found that as the platen moved towards the 

 central part of the bed the focus became more and more indistinct, indi- 

 cating that the central part was too low. The proper elevation was then 

 made at these points by means of heavy set-screws, when it was found that 

 the mercury was sharply in focus under the objective throughout the entire 

 range of motion. As a check upon the accuracy of the adjustment a 

 surface-plate 8 ft. in length was now planed, when it was found that the de- 

 viation from a true surface did not at any point exceed the third part of the 

 thickness of tissue paper. Two facts of considerable importance are to be 

 noticed in connection with this experiment. First, that the time occupied 

 for the complete adjustment was only twenty-five 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 ordi- 

 nary operations of turning shoulders to a given length, and of cylinders to 

 a given diameter, can be more expeditiously, more exactly, more econo- 

 mically performed than by the usual method. 



It is freely admitted by mechanicians that a decided advance in me- 

 chanical construction would be made by the employment of uniform 

 measures of length. This can be easily and profitably accomplished in any 

 well regulated shop, employing as many as fifty hands, by delivering from 

 a standards room any desired unit of length, in the same way that tools are 

 delivered from a tool-room. The expense of a comparator, from which any 

 measure 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 

 location, any workman could have a calliper 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 illus- 

 trations of the many ways in which the useful service of the Microscope 

 may be extended. 



In the address which I am called upon to make this evening, as Presi- 

 dent of the American Society of Microscopists, I have selected a single 

 application of the Microscope in scientific research. / heg 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 perpendicular distance 

 between the two faces may be said to represent a definite unit of length 

 at the temperature of 32° F. or of 0° 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 Breteuil 



