304 ANNUAL OF SCIENTIFIC DISCOVERY. 



The mass of the earth, according to the calculation of Baily, may be 

 reckoned at 6,000,000,000,000,000,000,000,000 kilogrammes. 



The matter of comets being assimilated above the air, of which the den- 

 sity would bo 45,000,000,000,000,000 times less than that of the ordinary air, 

 this would lead us to assimilate it to t'.ie substance of the earth diminished 

 to about 1 94,000,000,000,000,000,000,000 times less than its ordinary densi- 

 ty. By this estimate, a comet as large as the earth Avould only weigh 30,000 

 kilogrammes; this makes thirty tons of 1000 kilogrammes, or the weight of 

 thirty cubic metres of water. Comptes Rendus, 1857. Feb. 



In a subsequent paper presented to the Academic in May, 1857, M. Babi- 

 net enters into a calculation to ascertain the mass and density of the great 

 comet of 1825, which did not diminish the light of a star of the fifth magni- 

 tude seen through the centre of the comet, to the amount of one-fifth. His 

 conclusion, founded on the diminution which light undergoes in passing- 

 through air of known rarety, is that the substance of the comet of 1 825 pos- 

 sessed a density, which compared with atmospheric air at the surface of the 

 earth, must be indicated by a fraction, having unity of its numerator, and 

 for its denominator a number superior to unity, followed by one hundred and 

 twenty-five ciphers. 



When Hcrschel, in his last work on astronomy, spoke of a few ounces as 

 the mass of the tail of a comet, he found nearly as many disbelievers as 

 readers. Nevertheless, says M. Babinet, his calculation is exaggerated in 

 comparison with the preceding determination. M. Babinet promises, in a 

 future paper, to take up the very suggestive question, " How are comets 

 visible ? " 



CENTRAL RELATIONS OF THE SUN AND EARTH. 



BY C. F. WIXSLOW, M. D. 



In analyzing a record of 850 earthquakes and volcanic eruptions, collected 

 from all sources, the monthly tables read as follows : For 



April, 50 October, 95 



May, 47 November,. 95 



June, 44 December,.., 102 



July, 55 January, 94 



August, 64 February, 75 



September, 64 March, 65 



324 526 



By a glance at the above summary, it will be seen that the greatest number 

 of these events have occurred during the course of the planet through the 

 perihelic sections of its orbit ; that they increase steadily till the earth reaches 

 i!ie perihelion ; and then diminish, until at aphelion they are fewest. In this 

 respect these phenomena show a veiy steady and close inverse reference to 

 \\\Q length and sweep of the radius vector; and from this point of view, 

 holding unmistakable connection with well-known astronomical laws, they 

 become special results of solar causes. How do these causes operate ? 



One of the most remarkable facts in Robert Mallet's Report of 1851, to 



