Mr Whitelaw's Improved Grinding Machine, 335 



face, that which constitutes the colour of its cutting edge (Sa 

 colour de tranche), if I may be permitted to use this expression, 

 will strike perpendicularly the vertical ice of the prism ; it will 

 penetrate into the interior of this instrument, will traverse the 

 small quantity of air which it encloses, will reach the second 

 plate of ice, and will there be reflected vertically from below 

 upwards. In looking upon this inclined ice, the observer then 

 may judge of the proper colour which the water has by refrac- 

 tion, quite as well as if his eye were in the liquid. In this form, 

 the experiment is so simple and so easy, it requires so little 

 time that we shall venture to request the Academy to recom- 

 mend to our voyagers to repeat it as often as possible, not only 

 with sea-water, but also with that of lakes and rivers. When 

 the science shall be enriched with the results of all these obser- 

 vations, we shall no longer run the risk of constructing theories 

 which facts sooner or later will contradict. 



There is assuredly no occasion to remark that it is desirable 

 that the hollow prism should be enclosed at its upper part by 

 a piece of ice enclosed in glass, and having parallel faces. This 

 will prevent the apparatus from being filled with liquid. The 

 instrument can easily receive the form of the common instru- 

 ment from the hand of an artist. — Comptes Rendus, No. 4. 

 July 25. 1838. 



Description, with Drawings, of a Grinding Machine which is 

 used instead of a T^irning Lathe, Jbr giving a truly Cylin- 

 drical^rw to the rims of Pulleys and Drums : — also Draw- 

 ing and Description of a Machine for Grinding Pulleys 

 round on the rim. By Mr James Wiiitelaw. (Commu- 

 nicated by the Society of Arts.) With two Plates. 



Glasgow, 19/A January 1838. 



Gentlemen, — Mr Edward Sang, in his paper on the Pro- 

 gress of Exactitude in the Manufacture of Machines, has given 

 you an account of the latest improvements made on the turn- 

 ing, planing, and screwing machines. But besides these ma- 

 chines there is the grindstone, which has been fitted up of late, 



z2 



