B. TERRESTRIAL PHYSICS AND METEOROLOGY. 79 



Society by Professor Osborne Reynolds on the phenomena 

 of the refraction of sound by the atmosphere. Professor 

 Challis distinguishes the phenomena as those resulting from 

 fosr, and those due to the admixture of air and invisible va- 

 por. Assuming that fog, or haze, is due to the suspension in 

 the air of extremely minute globules of water, Professor Chal- 

 lis determines the velocity and condensation of the air due 

 to the reaction of a single small sphere on which acoustic vi- 

 brations are incident. He shows that, on account of the 

 small size of the globules, the reflection from a single globule 

 may be so extremely minute that the sum of the reflections 

 from a large number of globules may only generate reflected 

 waves of moderate magnitude, and apparently coming from 

 a great depth. Challis's theory points to no change in the 

 rate of propagation of sounds, but only to an alteration of 

 their intensity. But, passing to the effect of vapor in an in- 

 visible state mixed with the air, he shows that, whether this 

 vapor is connected with the air only by a kind of mechanical 

 suspension, or whether the mixture is so regular that there 

 are found changes of density more or less rapid as w T e pass 

 from point to point, without change of elasticity, it will still 

 happen that the air will be, in various degrees, impervious to 

 sound 7 A, 1874,XLVIL, 276. 



SUN-SPOTS AND TERRESTRIAL METEOROLOGY. 



Wolf, as the result of recent study on the influence of sun- 

 spots on temperature and rain-fall, states that he is brought 

 to the conclusion that, in the regular course of the sun-spot 

 phenomena, great frequency of sun-spots corresponds to lower 

 temperature and greater quantity of rain ; that, on the other 

 hand, at a time when the sun-spots and their variations en- 

 ter upon anomalous changes, these relations no longer hold, 

 but have almost the opposite character. Astron. Kach., 

 LXXXIII.,158. 



RAIX-FALL AND SUN-SPOTS. 



Wolf, of Zurich, has just published the results of a study 

 into the connection between sun-spots and rain-fall, on which 

 subject, indeed, lie has already published several valuable ar- 

 ticles. As his latest results, he states that he has investigated 

 the observations of rain-fall for Paris, Upminster, Bordeaux, 



