ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 4V> 1 



which he actually used appeared to the investigator so crude, and so Ear 

 from what preconceived notions of what such an apparatus should be, 

 that it was passed by as unworthy of notice. 



The late William A. Rogers of Cambridge (Mass.) devoted much 

 time and thought to the shaping of diamond points and edges for 

 ruling purposes, and had much success in ruling fine and close lines. 

 He took a great interest in what had been done by Nobert, and made 

 measurements of the latter's bands of lines. Rogers' observations 

 were published in the Proceedings of the American Academy of Arts 

 and Sciences. 



At that time the writer was interested in Roger's work, and it 

 struck him forcibly that Robert's bands could not have been ruled on a 

 machine like that used by Rogers. Quite a different principle must 

 have been employed. The writer went so far as to plan out an apparatus 

 involving the supposed principle. This apparatus he hoped some time 

 to make and put to the test. Its main features will be described, for we 

 will assume that some interest in these rulings still remains, and that 

 no better explanation of a method of ruling such bands of lines has yet 

 been published. 



The proposed method dispenses with all sliding ways, joints, and 

 screws. The ruling point is to be held by a light spring bar, its motions 

 controlled by electro-magnets ; and the spacing of the lines accomplished 

 by change of temperature of bars of dissimilar metals at measured time 

 intervals. 



In carrying out these conditions, a chronograph cylinder would be 

 used with contact points suitably disposed on its surface. Provision 

 would be made for heat storage in a medium surrounding the machine. 

 This apparatus would be placed in a room that could be kept at a 

 constant temperature. 



With this much provided, a preliminary trial of the ruling apparatus 

 would be made, and a line ruled at each revolution of the chronograph 

 cylinder during the fall in temperature. These preliminary lines would 

 be expected to diminish in distance apart from the beginning to the 

 end of the selected time interval, and they would afford the data for 

 calculation and measurement by which the final wwking electric contact- 

 points could be located. Success would depend upon the possibility of 

 repeating the temperature conditions, provided the chronograph worked 

 with precision. 



The ruling point is a vital part of the apparatus. Rogers' ex- 

 perience tended strongly to the use of ground and shaped points and 

 edges. It is expected, however, that, with the light pressure needed in 

 ruling these short bands covering a very small area, and with the 

 pressure controlled by a very light spring, a suitable working point 

 might be selected from minute chance-broken fragments of diamond. 

 A very delicate point might remain intact for a long time, since no 

 heavy moving parts would be involved as in a ruling machine. 



The errors in spacing and the curvature of the lines on a Nobert 

 diffraction grating were revealed by placing two photo copies so that 

 the film surfaces were in contact, and the lines on the two made nearly 

 parallel. Shaded irregular bands were thus produced indicating the 



