ASTRONOMICAL PHKtfOMENA AND PROGRESS. 



, on tho details of Mr. Stone's later ex- 

 i.-ut-. upon this subject with the great 



.rial of tho (Jrooinvirh Ohservatory. In 

 ling thorn, Mr. Stono constructed a ther- 

 ni.ipilo holi.-v.-.l liy him to bo superior to any 

 otlior previously invented. Ilia early trials 

 oonvinoeil him that it was almost impossible 

 M .li-tinguUh tho feeble effects generated by 



heat from the grosser effects produced 



upon the pile by exposure of one fuco within 



elescopo tube and tho protection of the 



face outside the tube. It was evident 

 that, to maintain tho pile in tho thermal 

 ei[uilihrhnn, its two faces must be exposed to 

 piveisely similar atmospheric intluenoes. Ho 

 tho iv tore made what may bo described as a 



star pile, tho two pieces of which, being 

 similarly presented to tho object-glass of tho 

 telescope, were affected alike by disturbing 

 causes, whether from currents of air or the 

 cooling of tho metals of the pile by radiation. 

 By this arrangement the whole heat of a star's 

 image cast upon either face of tho pile ma- 

 nipulated itself per se. Tho amount of heat 

 was measured by a reflecting galvanometer, 

 and the indications then converted into Fah- 

 renheit scale equivalents. It was found that 

 tho heating effect of Arcturus, after allow- 

 ing for absorption by tho object-glass, was 

 0.00000137 of a Fahrenheit degree, and that 

 of Alpha and Lyrra about two-thirds of that 

 amount. Otherwise expressed, the heat from 

 Arcturus, at an altitude of 25 at Greenwich, 

 is about equal to that of a three-inch cube of 

 boiling water at a distance of 400 yards, while 

 that from Alpha Lyra) is equal to the heat 

 from the same cube at 600 yards. Mr. Stone 

 conceives that the difference in the heating- 

 power may be connected in cause with differ- 

 ence of color. He finds that the manifested 

 heat diminishes rapidly as the amount of 

 moisture in tho air increases, and that all 

 sensible effect is cut off by the slightest cloud 

 or haze. (See ANNUAL CYCLOPAEDIA, for 1869.) 

 New Theory of the Milky Way. From a 

 careful examination of the structure of various 

 parts of the Milky Way, Mr. Proctor has been 

 led to the opinion that the true figure of the 

 system of stars constituting that zone is neither 

 a cloven disk, as supposed by Sir William 

 Herschel, nor a broad flat and in part cloven 

 ring, as suggested by Sir John Herschel. He 

 says that the existence of "coal-sacks," or 

 dark places, in the Milky Way suggests an idea 

 of its general figure. The coal-sacks cannot 

 be supposed to be tunnel-shaped openings ex- 

 tending through the whole breadth of a wide, 

 flat ring, without the "obvious improbability" 

 spoken of by Sir John Ilerschel when dealing 

 with the supposition that the nubocular way 

 is cylindrical in figure. If the coal-sacks are 

 really openings through a star zone, that zone 

 cannot in all probability have a much greater 

 extension in the direction of tho lino of sight 

 than at right angles to that line. According 

 to this view, the section of tho Milky Way 

 VOL. x. l A 



near tho coal-sacks in Crux (and presumably 

 elsowh' iv) would be roughly circular. Re- 

 garding tho Milky Way as a ring of circular 

 section that is, as resembling in section an or- 

 dinary wire ring one can understand many 

 peculiarities of its structure which seem wholly 

 opposed to either the disk or tho flat-ring 

 theory. For example, tho groat gap in tha 

 constellation Argo may bo readily explained, 

 and so may the yet wider vacant space in the 

 fainter branch when the ring is double. Mr. 

 Proctor shows how, by assigning to the Milky 

 Way a spiral figure, nearly all the principal 

 peculiarities of the zone can be very fairly ac- 

 counted for. Popular Science Review. 



Distribution of Stars. In a paper furnished* 

 by Mr. Proctor to the Popular Science Re- 

 view for July, he gives the result of his in- 

 quiries into the proportionate distribution of 

 stars in different parts of tho heavens. The 

 general results of a systematic survey of tho 

 stars of the first six magnitudes impel him 

 to conclusions like these : 1. The southern 

 hemisphere contains more stars of those mag- 

 nitudes than the northern, in the proportion 

 of about seven to five. 2. The stars of these 

 orders are gathered into two definite regions, 

 a northern and a southern, so markedly that 

 the distribution within those regions is richer 

 than that over the rest of the heavens, in tho 

 proportion of about five to two. 3. The stars 

 of these orders are associated in the most in- 

 timate manner with the Milky Way, insomuch 

 that, when the Milky Way is included with the 

 two rich regions referred to, it appears that 

 stars in the single division thus formed are 

 distributed about three times as richly as over 

 the remaining portions of the heavens. 



Apparent Size of Celestial Objects. N"o two 

 people would perhaps agree in attempting to 

 convoy an idea of the apparent size of any 

 celestial object say the moon. A pepper- 

 corn, a penny, a dinner-plate, a peck measure, 

 a cart-wheel, are some of the familiar objects 

 to which reference is made in the loose dis- 

 cussions of this subject. Mr. W. R. Grove 

 writes as follows to Nature : 



" About fifteen years ago I was looking at 

 Venus through a 40-inch telescope, Venus then 

 being very near the moon and of a crescent 

 form, the line across the middle or widest part 

 of the crescent being one-tenth of the plan- 

 et's diameter. It occurred to me to be a good 

 opportunity to examine how far there was any 

 reality in the estimate we form of the apparent 

 size of celestial objects. Venus through tho 

 telescope, with a magnifying power (speaking 

 from memory) of 135, looked about the size 

 of an old guinea, i. o., of a crescent cut off 

 from that coin. The moon, to my naked eye, 

 appeared the size of a dessert-plate. Having 

 fixed their apparent dimensions in my mind, I 

 adjusted the telescope so that with one eye I 

 could see Venus through the telescope, and 

 with tho other the moon without tho telescope, 

 and cause the images to overlap. I was greatly 



