ASTRONOMICAL PHENOMENA AND PROGRESS. 



45 



that which is moving less rapidly than itself, 

 and ia consequence will, so to speak, fall over 

 toward the east, the surface forming a gradual 

 slope to the east, and the fractured edges a 

 precipitous descent to the west. In the moon, 

 too, the author sees proofs of the contraction 

 continued long after the stage in which we 

 now find the earth. The spheroid of the moon 

 has contracted since it assumed that shape, 

 and, contracting less in the longer diameter, is 

 now more spheroidal than it should he accord- 

 ing to the theory, while the thickened crust, 

 no longer crushed down on the interior, has 

 left cavities in which the moon's ocean and 

 atmosphere are entomhed forever. 



The researches of Professor Kirkwood, of 

 Indiana University, by which he has brought 

 the asteroids into due correlation with the 

 other members of the solar system, and derived 

 from the relations which they present an argu- 

 ment in support of the nebular hypothesis, 

 are the subject of an interesting paper in 

 the Student for August, 1869, by Mr. Proc- 

 tor. The author regards Professor Kirkwood's 

 demonstrations as supplying a mathematical 

 proof of the formation of the asteriods from a 

 zone of cosmical matter, according to the pro- 

 cesses which Laplace conceived to have been 

 in operation ages ago, in the development of 

 the solar system. In the special instance of 

 the asteroids, these processes have not resulted 

 in the formation of a single planet ; but that 

 fact may be accounted for by the neighborhood 

 of so large a body as Jupiter. Had that planet 

 not been so near to the asteroid zone, the mat- 

 ter which composes the asteroids might have 

 united to form one planet. Such is Professor 

 Kir*kwood's view. But Mr. Proctor's theory 

 is somewhat different. He thinks that the 

 zone of the asteroids indicates the occurrence 

 of a definite change in the mode of evolution 

 of the planets. Up to that' point enormous 

 quantities of matter had been conglobing into 

 planets with noble systems of attendant orbs ; 

 indeed, there had been a pretty regular increase 

 from the masses of the giant planets Uranus and 

 Neptune, to the yet vaster Saturn, and to the 

 giant among giants Jupiter. Then the sub- 

 stance of the great revolving disk which had 

 given birth to those enormous bodies seems to 

 have been all but exhausted, so far as the gen- 

 eration of new orbs was concerned. The zone 

 next thrown off seems to have presented too 

 sparse an array of cosmical particles to form a 

 single planet by the action of its parts in pro- 

 ducing continual collisions, and so, with much 

 heat and turmoil, a vast rotating, molten, or 

 vaporous globe. With further contraction, the 

 disk seems gradually to have recovered its 

 planet-generating powers ; for first, the small 

 planet Mars was formed, then the Earth, with 

 actually an attendant moon. But there the 

 new effort culminated, the next planet Venus 

 being moonless, and appreciably smaller than 

 the Earth, and Mercury being the last and 

 least of the whole series. 



The Heat of the Stars. At a meeting of the 

 Royal Society, in February, Mr. Huggins read 

 a remarkable paper, narrating his experiments 

 to ascertain the heat of the stars. It had oc- 

 curred to him that the heat received on the 

 eartl; from the stars might possibly be more 

 easily detected than the solar heat reflected 

 from the moon. He therefore caused to be 

 prepared several thermopiles, and a very sen- 

 sitive galvanometer, and with this apparatus 

 succeeded in obtaining trustworthy indications 

 of stellar heat in the case of Sirius, Pollux, and 

 Regulus. His method of procedure was as fol- 

 lows : An astatic galvanometer was used, over 

 the upper needle of which a small concave mir- 

 ror was fixed, by which the image of the flame of 

 a lamp could be thrown upon a scale placed at 

 a distance. Usually, however, he preferred to 

 observe the needle directly by means of a lens 

 so placed that the divisions on the card were 

 magnified, and could be read by the observer 

 when at a little distance from the instrument. 

 To preserve the sensitiveness of the galvanome- 

 ter, a very careful adjustment of the magnetic 

 power of the needles was made from time to time. 

 So sensitive was the instrument, that the needles 

 would turn through 90 when two pieces of 

 wire, of different kinds of copper, were held 

 between the finger and thumb. The thermo- 

 piles consisted of one or two pairs of elements 

 alloys of bismuth and antimony being em- 

 ployed in some of the experiments. The ther- 

 mopile was attached to a refractor of eight 

 inches' aperture. Although some of the heat- 

 rays could not be transmitted through the ob- 

 ject-glass of the telescope, yet Mr. Huggins de- 

 cided that the more uniform temperature of 

 the air within the instrument, and some other 

 circumstances, would make the difficulty of 

 preserving the pile from extraneous influences 

 less formidable than if a reflecting telescope 

 were used. The apparatus was fixed to the 

 telescope so that the surface of the thermopile 

 would be at the focal point of the object-glass, 

 and was allowed to remain attached to the tele- 

 scope for hours, and sometimes for days, the 

 wires being in connection with the galvanome- 

 ter, until the heat had become uniformly dis- 

 tributed within the apparatus containing the 

 thermopile, and the needle remained at zero, 

 or was steadily deflected to the extent of a 

 degree or two from zero. When observations 

 were to be made, the shutter of the dome was 

 opened, and the telescope, by means of the 

 finder, was directed to a part of the sky near 

 the star to be examined, where there were no 

 bright stars. The needle was then watched, 

 and, if in four or five minutes it had experi- 

 enced no deviation, then, by means of the find- 

 er, the telescope was moved, the small distance 

 necessary to bring the image of the star exactly 

 upon the face of the pile, where it was kept by 

 means of the clock-work attached to the tele- 

 scope. Almost always the needle began to 

 move as soon as the image of the star fell upon 

 it. The telescope was then moved so as to di- 



