No. 9. {From the Philosophical Magazine, 1895, S. 5, Vol. XZ,, 

 PP- 153-172.] 



ON THE USE OF THE GLOBE IN THE 

 STUDY OF CRYSTALLOGRAPHY 1 



THE use of the globe in Crystallography is twofold. It 

 enables us to study the character and follow the details of 

 the form of the solid projected radially on its surface. Also 

 all the measurements which can be made on the solid itself 

 can be as conveniently made on its projection on the sphere, 

 and all calculations and developments connected therewith 

 can be made by simple graphical construction and measure- 

 ments on the sphere. The black globe, with the divided circles 

 belonging to it, is a calculating machine adapted to the solution 

 of all the problems to which the analytical methods of spherical 

 trigonometry are usually applied. 



To the student of crystallography, of astronomy, of mathe- 

 matical geometry, and of geometry of three dimensions 

 generally, the globe and its circles fill the same place as the 

 drawing-board and scale do to the engineer and surveyor. A 

 globe which is to be used for geometrical constructions should 

 be quite free and unencumbered with the fixed axis usually 

 met with in those intended for geographical or astronomical 

 instruction. Also the divided circles with which measure- 

 ments are made should be capable of being applied directly 

 to the surface of the globe, so as to avoid errors of parallax. 

 The globe which I have found most suitable for the purpose, 

 and I have used it for a number of years, is one published 

 by Mr E. Bertaux, of 25 Rue Serpente, Paris. It has a 

 diameter of 22 centimetres, and has either a black surface 

 for drawing on with slate pencil or chalk, or a white 



1 Read before the Chemical Society, December 6, 1894. 



