ASTRONOMY AND METEOROLOGY. 381 



even with Arago's polariscope, with a double-colored image. But 

 on July 3d, and the following days until the 7th, the nucleus, in spite 

 of its extreme diminution, exhibited sensible indications of polariza- 

 tion. Father Secchi considers this fact of great importance, since it 

 thereby appears that the nucleus in the first instance transmitted its 

 own light, perhaps on account of the incandescence to which it was 

 raised by its near propinquity to the sun. 



RELATIVE BRIGHTNESS OF THE SUN AND MOON. 



The ratio between the light received at the earth from the sun and 

 the full moon has been very differently estimated by two different 

 and eminent observers, namely, Bouguer, a French astronomer, and 

 Wollaston, the well-known English physicist. The former estimated 

 the brightness of the sun to be three hundred thousand times greater 

 than that of the moon ; while the latter fixed it at eight hundred and 

 one thousand and seventy-two times greater. This great discordance 

 of results having excited a doubt as to the value of the process fol- 

 lowed by the above-named experimenters in working out their prob- 

 lem, Prof. George P. Bond, of the Cambridge (Mass.) Observatory, 

 has, during the past year, re-examined the whole subject, and ar- 

 rived at new and probably more accurate results than any before 

 attained to. 



The method of Bouguer is thus described by Arago : " On the day 

 of observation, the sun being at an altitude of thirty-one degrees, 

 and his rays entering a dark chamber through a hole one-twelfth of 

 an inch in diameter, he placed a concave lens in front of this aperture, 

 which diminished the intensity of the solar rays by causing them to 

 diverge. Then, receiving this divergent light on a screen, at a dis- 

 tance where it was weakened in the proportion of 1 to 11,664, he 

 found it equal to that of a candle situated at the distance of seven- 

 teen inches from the screen. Repeating this experiment at night 

 with the moonlight and the same concave lens, the moon being full, 

 and also at an altitude of thirty-one degrees, Bouguer perceived that 

 the light, when it had been made to diverge seven-tenths of an inch, 

 or when it had been weakened only by one sixty-fourth, was already 

 so faint that the candle had to be put at a distance of 53.2 feet be- 

 fore the two lights could be rendered equal. Hence we find by a 

 suitable calculation that the sun illuminates the earth's surface 256,289 

 times more than the moon does. Three similar experiments, made at 

 various seasons of the year 1725, yielded the following results to M. 

 Bouguer: 284,089; 331,760; 302,500. Whence the celebrated aca- 

 demician concluded that the proportion of sunlight to moonlight, 

 when the moon is at her mean distance, is as 300,000 to 1." 



Wollaston furnishes the following account of his mode of proce- 

 dure : 



" The sun's light was compared with that of a candle, by admitting 

 a beam of it into a room through a small circular hole in a plate of 

 metal, fastened in a window-shutter; and a small cylinder of any 

 opaque material being placed in the beam, so as to cast a shadow 

 upon a screen, the distance of a candle from the same cylinder (or an 

 equal one placed at the same distance from the screen) was varied, 



