14 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



to a great extent independent of its lighter envelope. The 

 photosphere, according to these authors, is subject to period- 

 ical variations, which are not directly due to the force of 

 gravitation. The force which specially deforms the pho- 

 tosphere is intimately connected with that which affects the 

 secular movement of the centre of gravity of the sun, as has 

 been shown by Le Verrier. The secular changes of the pho- 

 tosphere and of terrestrial magnetism are subject to a simul- 

 taneous oscillation of sixty-six and two-third years, similar 

 to that equal period to which the perigeum of the apparent 

 solar orbit is subject. 19 C, VIII., 33. 



ON SOLAR RADIATION. 



One of the most comprehensive investigations into the 

 subject of solar radiation is that recently published by the 

 Rev. F. W. Stowe, based on five years' observations at 

 twenty-five stations, with the black bulb maximum ther- 

 mometer in vacuo, freely exposed to the sun and air at 

 the height of at least four feet. By the amount of solar 

 radiation, he understands the excess of the reading of the 

 solar thermometer above that of the ordinary maximum 

 thermometer placed in a double -louver screen. Incident- 

 ally he mentions that the solar thermometer seldom reads 

 above 140 Fahr. in England, and that 134 is the high- 

 est temperature on his records. The radiation attains its 

 maximum in May. This is to be attributed to the preva- 

 lence of northerly winds, and consequent dryness of the at- 

 mosphere. December is the month of least radiation. In 

 this statement we take account only of the maximum amounts 

 of radiation during clear days in those months. The west- 

 ern stations in England show more radiation than the east- 

 erly ones. The neighborhood of the sea appears to some- 

 what diminish solar radiation during the summer, which he 

 attributes to the fact that the air from the sea is, for the 

 most part, heavily loaded with vapor during the summer 

 season. The excess of radiation at western stations, lie is 

 inclined to attribute to the greater purity and coolness of 

 the air, and its freedom from haze. As regards secular 

 change, he found the radiation decidedly in defect in the 

 early summer of 1870, but in excess in 1872, a result which 

 may have resulted from the presence of a colder stratum 



