ASTRONOMY AND METEOROLOGY. 289 



forming that tingle being the terrestrial radius, and the other 

 a line that joins the centre of the earth with that of the sun, it fol- 

 lows that, as we know the radius and right angle, the third ele- 

 ment we want in order to determine the distance of the two 

 centres is precisely the angle made by the latter and the hypothe- 

 nuse drawn from the centre of the sun to the extremity of the 

 earth's radius ; and that is precisely the parallax. 



Without knowing that we cannot, therefore, know our own dis- 

 tance from the sun, and consequently, by Kepler's third law, the 

 distances of the planets either. Such is the importance of that ele- 

 ment that Encke, in 1835, recalculated it from the transit of 

 Venus in 1769, and found it to be 8.58 sec. M. Leverrier finds 

 this value too small on theoretic grounds, and states it at 8.95 

 sec. By the aid of the apposition of the planet Mars, which 

 occurred in 1862 under remarkably favorable circumstances, a 

 combination of observations simultaneously made at the Cape of 

 Good Hope and at Pulkowa, the parallax was found to be 8.964 

 sec. M. Pauwalki, of Berlin, finds it only 8.86 sec. From these 

 various results it is clear that there is an uncertainty as to the 

 value of the parallax amounting to nearly three-tenths of a sec- 

 ond, a considerable figure in such an enormous distance as that 

 existing between the sun and the earth ; and it is hoped that the 

 coming transits of Venus will be attended with circumstances 

 favorable enough to determine the exact value sought. 



THE SUN'S SPOTS. 



The astronomers of Kew Observatory have been engaged in ob- 

 servingand comparing, from time to time, the spots on the sun, with 

 a view of discovering some cause with which their changes may be 

 connected. They have found that the expansion and contraction 

 of the spots proceed at a regular rate according to their varying 

 position in the apparent disc; the spots increasing invariably from 

 left to right, and attaining their maximum at intervals of about 



19 or 20 months. The revolutions of the planet Venus, which 

 proceed in like manner from left to right, and occupy also about 



20 months, were next compared with the changes in the spots, 

 and were found to correspond. The area of spots exposed to view 

 toward the earth was found to be uniformly greatest when Venus 

 was on the opposite side of the sun, and least when the observed 

 side was exposed most directly to her influence. Jupiter also, 

 from its great mass, exercises an influence upon the spots, al- 

 though from its distance it is not predominating. When Jupiter 

 and Venus were both in opposition to the earth, the spots were 

 much more enlarged than when Venus was in opposition and 

 Jupiter in conjunction with the earth. The nature of the influ- 

 ence evidently exerted is thought to be suggested in an opinion 

 expressed by Prof. Tate, "that the properties of a body, es- 

 pecially those with respect to heat and light, may be influenced 

 by the'neighborhood of a large body; " and an influence of this 

 kind would naturally be most powerful upon a body possessed of 

 a very high temperature, like the sun ; a very small increment 



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