1869.] 



President's Address. 



109 



Some idea of the enormous amount of labour bestowed upon these re- 

 searches may be formed from the fact, that not fewer than eighty-four ex- 

 periments were made upon the specific heat of air, under different pres- 

 sures and temperatures, forty-three upon aqueous vapour, twenty-four 

 upon carbonic acid, and a considerable number upon other important 

 gases and vapours, embracing no fewer than thirty-six different elemen- 

 tary and compound bodies, many of which required special modifications 

 of the method and apparatus employed. 



Besides this remarkable series of researches, M. Regnault has embodied 

 in his work : — investigations on the compressibility of gases under wide vari- 

 ations of pressure, and on the specific heat of liquids at different tempera- 

 tures ; also a second memoir on the elastic force of saturated vapours at 

 different pressures, which he has extended to the compressed gases, and to 

 the density of vapours emitted by saline solutions and by mixed liquids. 

 In addition to all these, he has a memoir on the latent heat of vapours at 

 different tensions. 



This extended series of investigations is carried out with minute and 

 scrupulous precision, and the sources and limits of error are traced and 

 guarded against with unvarying skill and sagacity. The publication of 

 this work, the greatest experimental contribution of any single individual 

 to the science of heat, must indeed mark an era in the history of thermotics, 

 and furnish data of enduring value both to the chemist and the physicist 

 in all that concerns specific and latent heat, and the laws of elastic force 

 as acting on aeriform bodies. 



Professor Miller, 

 We greatly regret that we are deprived of the pleasure of Monsieur 

 Regnault' s presence by reason of illness in his family. I will there- 

 fore request you to receive the Medal on his behalf, and to transmit it to 

 him with the assurance of the Society's highest respect. 



The Council has awarded a Royal Medal to Sir Thomas Maclear, Astro- 

 nomer Royal at the Cape of Good Hope, for his Measurement of an Arc 

 of the Meridian at the Cape of Good Hope. 



Our sole knowledge of the figure of the southern hemisphere rests on the 

 arc of the meridian measured by La Caille, and now remeasured and ex- 

 tended by Maclear. The original measurement, notwithstanding the well- 

 known ability of the great astronomer under whose superintendence it was 

 executed, has not commanded confidence. The magnitude of the degree 

 inferred from it is far too great, and, if accepted, would lead to the con- 

 clusion that the dimensions of the two hemispheres are dissimilar. But 

 La Caille' s angles were observed with a quadrant, not with a circle, and 

 were therefore liable to errors of eccentricity and of figure ; while the 

 effects of local attraction, if recognized at all, were very imperfectly ap- 



