238 Mr. Blakesley on a Method of obtaining 6 from 



of Angstrom the effect of radiation is minimized by (1) using 

 bright bars, (2) by making the period of the end variation 

 small, (3) by measuring axial temperatures of a fairly thick 

 rod. The radiation can be made negligible while the essence 

 of the method is not affected. In the class of problems here 

 considered, on the other hand, if we diminish the radiation 

 beyond a certain point we nullify the thermal equation alto- 

 gether, and 'get a' problem requiring a different treatment. 

 The essential point is that the radiation should be small, but 

 not so small as to be ineffective. 



I have to acknowledge with pleasure kind suggestions and 

 criticisms from Professor Gray in the preparation of this 

 paper. 



Glasgow University, May 8th, 1902. 



XXVI. On a Method of mechanically obtaining 6 from the 

 Hyperbolic Trigonometrical Functions of 6, By T. H. 

 Blakesley, M.A., MJnst. C.E* 



LET A B C be a triangle having a right angle at C ; and 

 let a, b, c be the sides opposite the angles A, B, C. Let 

 b be constant. 



Fig. 1. 



The point B is supposed to travel from the point C, and 

 therefore a is the independent variable. D is a point in this 

 line of motion infinitesimally near to B, and BE isi a perpen- 

 dicular from B upon the line A D. 



Then it is clear that if 6 is such a quantity that 



a = b shin 0, it will also be true that 

 c = b cosh 6, because 



* Communicated by the Author, 



