1886.J 



President's Address. 



385 



necting the mean deviation of some condition (such for example as 

 stature) in a series of individuals from the general average with the 

 mean deviations of the same condition in the relatives of those same 

 individuals of different kinds, such as fathers, brothers, &c. Nor is 

 the statistical method applicable to bodily characteristics alone. Mr. 

 Galton has even extended it with remarkable ingenuity and originality 

 to mental phenomena also. 



The Rumford Medal has been awarded to Professor Samuel P. 

 Langley, for his researches on the spectrum by means of the bolo- 

 meter. 



A better knowledge of the ultra-red region of the spectrum, which 

 includes the larger part of the energy of solar radiation, had long 

 been a desideratum, when Professor Langley commenced his work 

 upon this subject. Finding the thermopile insufficiently sensitive for 

 his purpose, he contrived the " bolometer." This instrument depends 

 upon the effect of temperature upon the electrical resistance of metals, 

 a quantity susceptible of very accurate measurement ; and, with its 

 aid, Professor Langley has been able to explore a part of the spectrum 

 previously almost inaccessible to observation. 



A res alt of Professor Langley 's work, very important from the 

 point of view of optical theory and of the ultimate constitution of 

 matter, relates to the law of dispersion, or the dependence of refran- 

 gibility on wave-length.. Cauchy's formula, which corresponds well 

 with observation over most of the visible spectrum, is found to break 

 down entirely when applied to the extreme ultra-red. 



Professor Langley has given much attention to the important ques- 

 tion of the influence of the atmosphere on solar radiation. The 

 expedition to Mount Whitney, successfully conducted by him in face 

 of many difficulties, has given results of the utmost value, pointing to 

 conclusions of great interest and novelty. 



The Davy Medal has been awarded to our foreign member, M. 

 Jean Charles Galissard de Marignac, for his researches on atomic 

 weights. 



M. Marignac's numerous researches on atomic weights, which have 

 been continued for a great number of years, have played an exceed- 

 ingly important part in establishing and consolidating that ground- 

 work of chemistry. They are remarkable for originality in devising 

 methods appropriate to the respective cases, the most conscientious 

 care in discovering errors which occurred in the respective operations, 

 and indefatigable perseverance in finding" means to eliminate the 

 disturbing influences. His labours are all the more valuable because 

 he chose for their field chiefly those elements which are most generally 

 used in chemistry, and are most important to chemists, and on which 

 the determination of new atomic weights is most generally made to 

 depend. 



