36 



ASTRONOMY, PROGRESS OF, IN 1892. 



read before the meeting of the American As- 

 sociation for the Advancement of Science, at 

 Rochester, in August, he described the ingenious 

 apparatus which he had invented and perfected 

 for photographing the spots, the faculae, and the 

 prominences. This device records faculre which 

 the eye can not detect. He secures on one plate, 

 with one exposure, the spots, facula?, chromo- 

 sphere, and the protuberances, and exhibited be- 

 fore the association, by the aid of the optical 

 lantern, the first complete picture of the sun 

 ever taken. The reader will find a description 

 of the spectroheliograph in " Astronomy and 

 Astro-physics" (late " Sidereal Messenger ") for 

 May, 1892, published at Northfield, Minn. 



Prof. Bale's achievement in photographing ten 

 bright lines heretofore unknown in the ultra- 

 violet spectrum of the prominences and the 

 chromosphere is an unrivaled one, and excites 

 great interest among astronomers and spectros- 

 copists. By the aid of a new objective by Bra- 

 shear, which by its color correction is well adapt- 

 ed to this kind of work, he has photographed 

 nineteen lines in the ultra-violet. 



A photograph of importance was taken on 

 July 15, showing simply a large spot. A few 

 minutes later another was secured in which a 

 bright band had developed. Twenty-seven min- 

 utes after the last named, another plate showed 

 bright faculae covering nearly the entire spot, 

 which, however, soon disappeared, and the spot 

 at the final exposure presented the same appear- 

 ance as on the first plate. The accurate photo- 

 graphic delineation of such sudden changes is 

 justly regarded as greatly important. On the day 

 following these observations, a magnetic disturb- 

 ance and brilliant aurora were noted. Prof. Hale 

 estimated the size of the spot to have been 4,000,- 

 000,000 square miles. 



The Sun's Diameter. In Astronomische Nach- 

 richten, No. 3,066. Dr. Auwei's gives the results 

 for solar parallax from the German transit-of- 

 Venus expeditions in 1874 and 1882. That of 

 the transit of 1874 is 8*877" 0-043, and that of 

 1882 equals 8'879" 0'037. 



In the same journal, No. 3,068, the same writer 

 has a paper on the diameter of the sun as deter- 

 mined by the heliometric measures made in con- 

 nection with the above-named expeditions by 31 

 observers with 4 instruments. He finds the mean 

 results for the sun's mean diameter to be 1,919-3", 

 which differs considerably from that at present 

 adopted by the various nautical almanacs, the 

 German being 1,922'4", the French and English 

 1,923-6", and the American 1,924'0". Dr. Auwers 

 remarks that, if the value he finds is influenced 

 by irradiation effects, it can only be too large, 

 and thus the errors of the adopted diameters 

 must be greater still. He urges that an imme- 

 diate change in these values be made, and an- 

 nounces for the " German Almanac " that the 

 alteration will occur in the volume for 1895. 



The observations are discussed for possible 

 ellipticity of the sun's disk, with the result that 

 the polar diameter is found to exceed the equa- 

 torial by 0-032. Had the personalities of the ob- 

 servers, in both perpendicular and horizontal 

 observations, been taken into consideration, the 

 value for the polar diameter, it is believed, would 

 have been less, as indeed it ought to be, consid- 

 ering the sun as a rotating body. But an ellip- 



ticity of so small an amount as 0-038" is im- 

 measurable, and indicates that a deviation from 

 an exact sphere has not been and can not be 

 proved. 



The Cause of Solar Heat. In the recently 

 issued volume of " Transactions of the Astro- 

 nomical and Physical Society of Toronto," Dr. 

 Joseph Morrison, of the "American Nautical 

 Almanac " office, has a paper treating of the two 

 most generally received theories of the source 

 and maintenance of the enormous heat of the 

 sun. One hypothesis is that it is due to the en- 

 ergy developed by the falling of meteoric matter 

 on the sun. The other asserts that it is produced 

 and kept up by slow contraction of the sun's 

 bulk. He calculates that a pound of matter fall- 

 ing from infinity would develop 82,340,000 units 

 of heat, and, therefore, that a quantity of matter 

 equaling one one hundredth of the earth's mass 

 falling annually on the sun would maintain an 

 amount of heat equal to that observed. 



As to the contraction theory, he says, taking 

 the solar constant at 25 calories per square metre 

 per minute, the linear contraction of the sun's 

 radius requisite to keep up the present radiation 

 is 156-9 feet in a year, or nearly 30 miles in a 

 thousand years. As 450 miles of the sun's diam- 

 eter subtends, at the earth's distance, an angle 

 of only one second of arc, it would, therefore, re- 

 quire 7,575 years for the sun's angular diameter 

 to be reduced by one second of arc, the smallest 

 angle measurable on the sun's disk. 



Direction of the Sun's Motion. A little more 

 than a hundred years ago Sir William Herschel, 

 noticing that the stars in the constellation Her- 

 cules were slightly farther apart, and that those 

 in the opposite direction were nearer together 

 than as determined prior to his day, came to the 

 conclusion, and so announced, that our sun, with 

 the entire solar system, had a progressive mo- 

 tion in the direction of Hercules. This theory 

 has never, from subsequent observation, been 

 disputed, save as to the exact direction of its 

 motion. 



Prof. Lewis Boss, Director of the Dudley Ob- 

 servatory, has exhausted the refinements of 

 mathematical and observational astronomy only 

 to establish its truth. He, however, places, as 

 the result of his calculations, the "apex of the 

 sun's way" in R. A. 289 ; Dec. + 51, or in Cyg- 

 nus instead of Hercules. 



McStumpe has likewise made thorough inves- 

 tigation of the complex problem, but his results 

 differ somewhat from those of Prof. Boss. His 

 mean of four determinations gives R. A. 285 ; 

 Dec. north 36, or between Cygnus and Hercules. 



The Moon. Lunar Radiant Heat. The sec- 

 ond series of Vol. IV of the Scientific Transac- 

 tions of Royal Dublin Society contains a memoir 

 on the moon's radiant heat as determined by Dr. 

 Boeddicker at the observatory of Lord Rosse, Birr 

 Castle, Ireland, during the total lunar eclipse of 

 Jan. 28, 1888. His conclusion was that the moon's 

 heat has much lower refrangibility than the sun's, 

 and that the maximum of heat falls rather before 

 than after the time of full. The results of this 

 eclipse fully confirmed those of that of 1884, the 

 radiation falling considerably below the com- 

 mencement of the eclipse and not returning to 

 its standard value until l h 40 m after last contact 

 with the penumbra. He considers the fact es- 



