S70 SURVEY OF THE COAST 



these measurements has yet been made, on account of the 

 interruption necessary in order to make the pyrometric ex- 

 periments before the breaking up of the winter. The mi- 

 crometer values indicated in the results are however cor- 

 rected for the above value, and represent therefore actual 

 decimals of the individual subdivision mentioned. From 

 this circumstance, the comparison remains confined to the 

 distance used on the scale ; but it may easily be extended, 

 by measuring this distance, as indicated, on as many other 

 parts of the scale as admissible ; and the difference will 

 probably not be much. 



When the microscopes were screwed fast in their places, 

 the 0° point of the micrometer did not exactly agree with the 

 division of the scale from which it was intended to read. In- 

 stead of adjusting it by the screw which guides the slider 

 of the micrometer and the divided head of the screw, I pre- 

 ferred ascertaining carefully the point of coincidence on the 

 division and on the micrometer, and to adopt tliis last as the 

 0° point of the micrometer, from which the divisions were to 

 be subtracted, since the micrometer was read from 78",8 

 backwards, or by subtraction. The point so determined 

 was 78",8001375; or the actual distance from which the 

 readings were subtracted was 76",8001375. 



The repetition of the comparisons with the microscopic 

 readings direct, which I had also the intention of making, 

 was prevented by the circumstances stated above ; and 1 

 never afterwards could bestow any time upon this subject, 

 before the collection left my hands. 



The abridged notations for the registering of the compa^ 

 risons are as follows : — 



C denotes the toise of Canivet. 



L Lenoir. 



i* the copy of the toise of Lalande marked A. 



l^ the same marked B. 



the inversion of the letters denoting that the marks on the 



