24 ANNUAL KECOKD OF SCIENCE AND INDUSTRY. 



the transit, as given by the British Nautical Almanac, and to 

 subtract the product from 31' 3.64". Applying this rule to 

 the observations published by the Royal Observatory of 

 Greenwich for sixteen years (from 1853 to 1869), he deduces 

 a series of results which lead him to investigate the question 

 of the variability of the diameter of the sun; a problem that 

 had been approximately resolved, a few months previous, by 

 Fathers Secchi and Rosa. He finds, however, that the dis- 

 cordances in his results are plausibly attributed, not to a va- 

 riability in the sun itself, but to the variability in the con- 

 dition of the earth's atmosphere, and to the peculiarities of 

 the eyes of different observers; and expresses his exact result 

 in the following terms : The mean correction to the diam- 

 eter of the English Nautical Almanac (32' 3.64") is 2.807", 

 with a probable error of 0.193", when the number expressing 

 the atmospheric enlargement is 2, and that expressing the oc- 

 ular irradiation is 5. Applying his rules to seventy-five ob- 

 servations made by himself in 1872, for which the number on 

 the scale expressing the atmospheric enlargement is 7, he 

 finds the solar diameter referred to the mean distance of the 

 earth to have a mean value of 31' 57.3", with a probable er- 

 ror not surpassing l"; and asserts that he has every reason to 

 believe that the diameter of the sun is notably less than that 

 usually adopted by astronomers, and approximately equal to 

 the number just given. Atti delta II. Accad. Scienze, Turin^ 

 1873, Part VIIL, p. 587. 



THE SATELLITES OF JUPITER. 



Professor Alexander, of Princeton, suggests that an ex- 

 planation, better than the common ones, may be given of 

 the peculiar phenomena exhibited by certain satellites of 

 Jupiter, which, as they pass over the disk of the planet, be- 

 come apparently much fainter, and even black, in compar- 

 ison with the bright body of the planet. He thinks that the 

 phenomena seems to be the result of the absorption and in- 

 terference of the vibrations of light, on a scale such as only 

 astronomy exhibits. He also concludes that the temperature 

 of the surface of the obscure-looking satellites must be lower 

 than that of the atmosphere, or at least of the body of the 

 planet ; and, finally, that the satellites which exhibit these 

 very remarkable phenomena have no atmospheres, and are, 



