478 Intelligence and Miscellaneous Articles. 



I must be permitted, in concluding this note, to thank M. Ruhm- 

 korff for the kindness with which he has" been pleased to place at 

 my disposal, for the experiments described, a differential galvano- 

 meter of very great delicacy. — Oomptes Rendus, October 22, 1866. 



ON AQUEOUS VAPOUR AND SOLAR RADIATION. 

 [Extract of a Letter from M. Soret to Prof. Tyndall.] 

 During the past summer I have made some experiments on solar 

 radiation. The bulb of a thermometer was placed in a cavity sur- 

 rounded by ice, in order to prevent any agitation of the air, and to 

 preserve the surrounding temperature constant. The solar rays fell 

 directly on the bulb of the thermometer, which was first varnished 

 and then coated with lampblack. In two comparative experiments 

 made within a few days at Geneva and Bologna, the most powerful 

 radiation was obtained at Geneva, although at Bologna the heavens 

 were visibly purer. The result appears to me to support your views 

 regarding the aqueous vapour of the air ; for the tension of aqueous 

 vapour at Bologna was 10*7, while at Geneva it was only 6'33. I 

 have, however, made only one observation, my thermometer having 

 been broken in returning. The single fact is not sufficient to enable 

 me to draw a certain conclusion.' 



L. SORET. 



Geneva, Nov. 13, 1866. 



ON THE INFLUENCE OP THE EARTH S ROTATION ON THE DEVIA- 

 TION OF PROJECTILES FROM RIFLED CANNON. BY M. MARTIN 

 DE BRETTES. 



The distinguished geometrician Poisson treated this question in 

 1837 for the case of spherical projectiles, and has drawn the follow- 

 ing conclusions : — 



(1) The ranges vary with the azimuths of the plane of firing, but 

 between very narrow limits ; for the greatest variation would be two 

 decimetres for a range of 1800 metres in firing from a mortar. It 

 would be still less in firing point blank ; so that, practically, the in- 

 fluence of the azimuth of the plane of fire on the ranges is zero. 



(2) The influence of the rotation of the earth in our hemisphere 

 causes a deviation of the projectiles to the right of the plane of firing, 

 whatever be its azimuth. This deviation, whose magnitude is 

 independent of the azimuth of the plane of firing, may attain a con- 

 siderable value. Thus, from Poisson's calculations, a bomb of 32 

 centims. ;diameter at 4000 metres would deviate 8 metres in our 

 latitude, owing to the rotation of the earth. 



(3) The deviation increases with the latitude ; it is greatest at 

 the poles, and zero at the equator. 



The influence of the earth's rotation on the aim of the firearms 

 then used was very small relatively to that of the accidental causes 

 which caused considerable variations in the direction and range from 



