Presidents A ddress, 313 



radiometer, an instrument rivalling the bolometer in the measurement 

 of small amounts of radiation. Its sensitiveness and accuracy were ob- 

 tained in part by the use of a quartz fibre to suspend the coil, in part 

 by the admirable design of every portion of the instrument. Professor 

 Boys was the first to show its value in an investigation into the 

 radiation received from the moon and stars. 



In his great research on the value of the Newtonian constant of 

 attraction, Professor Bovs used quartz fibres to measure the gravitation 

 forces between small bodies by the Mich ell- Cavendish torsion method. 

 He redesigned the whole of the apparatus, and, calculating what 

 should be the dimensions and arrangements to give the best results, 

 he was led to the remarkable conclusion that accuracy was to be 

 gained by a very great reduction in the size of the apparatus. This 

 conclusion he justified by a determination of the value of the New- 

 tonian constant, which is now accepted as the standard. 



Professor Boys has also made some remarkable studies by a photo- 

 graphic method of the motion of projectiles, and of the air through 

 which they pass. 



All his work is characterised by the admirable adjustment of. 

 the different parts of the apparatus he uses to give the best results. 

 His instruments, are, indeed, models of beauty of design. 



RUMFORD MEDAL. 

 Professor Philip P. Lenard and Professor W. C. Rontgen. 



In tlr^ case of the Rumford Medal, the Council have adopted a 

 course, for which there are precedents in the awards of the Davy 

 Medal, but which is, as far as the Rumford Medal itself is concerned, 

 a new departure. They have decided to award the Medal in dupli- 

 cate. It has often happened in the history of science that the same 

 discovery has been made almost simultaneously and quite indepen- 

 dently by two observers, but the joint recipients of the Rumford 

 Medal do not stand in this relation to each other. Each of them may 

 fairly claim that his work has special merits and characteristics of 

 its own. To day, however, we have to deal, not with points of 

 difference, but with points of similarity. There can be no question 

 that a great addition has recently been made to our knowledge 

 of the phenomena which occur outside a highly exhausted tube 

 through which an electrical discharge is passing. 



Many physicists have studied the luminous and other effects which 

 take place within the tube ; but the extension of the field of inquiry 

 to the external space around it is novel and most important. There 

 can be no doubt that this extension is chiefly due to two men Pro- 

 fessor Lenard and Professor Rontgen. 



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