April 13, 1876] 



NATURE 



467 



greatest efTect observable in the differences of the earth's mag- 

 netism ? 



Third : Are the sun-spots caused by clouds or curtains out- 

 side, and hiding the apparent surface of the sun, or are they 

 deep cavities through the same ? Stephen W. Allen 



Boston, U.S.A., March 27 



Metachromism 



I REFRAIN from replying to Mr. Petrie's second letter (p. 426) 

 until after the appearance of the article to which Mr. Costerus 

 refers (p. 427) on "Organic Colour Change." 



In defence of Miller, however, I would just add that on p. 298, 

 vol. ii. (filth edition), occur the following words : — "The sodic 

 dioxide, Na^Oj, obtained by igniting sodium in oxygen is of a 

 pure white colour." \Vm. AckroYD 



Royal ColL of Chemistry, South Ken ington, April 3 



Dr. Klein on the Small-pox of Sheep 



I WRITE this note in order to inform you that, my attention 

 having been directed to some alleged fallacies in some of my 

 observations regarding the small-pox of sheep, I am at present 

 engaged in reinvestigating the subject. E. Klein 



The Brown Institution, April 11 



OUR ASTRONOMICAL COLUMN 



Olbers' Supposed Variable Star near 53 Vir- 

 gin is. — The only comet detected in the year 1796 was 

 found by Olbers in Virgo on the night of March 31. On 

 the following evening, at 8h. 55ni., apparent time at 

 Bremen, it was over a star of the seventh magnitude 

 south — following 53 Virginis, and the light of the star 

 was remarked to be little affected by the intervention of 

 the comet. On March i, 1797, desiring to fix more 

 exactly the place of this star, Olbers found in its position 

 one of only the tenth or eleventh magnitude, whereas in 

 April previous, according to Schroeter, who appears to 

 have compared the comet with it early on the morning of 

 April 2, it was the brightest star in the immediate neigh- 

 bourhood of 53 Virginis, and hence in Olbers' judgment 

 '• a seventh magnitude at least.'" Writing to Bode in 

 March 1797 he directs attention to this star, as perhaps a 

 more remarkable variable star than even x Cygni. The 

 circumstances preclude suspicion of a similar phenomenon 

 to that described by Piazzi when the great comet of 181 1 

 passed over his star XX. 197, 



From the positions of the supposed variable, and its 

 neighbours given by Olbers (who also appends a diagram), 

 it is evident that his star, which followed 53 Virginis 

 30' 55" in RA., 20' 45" to the south, is No. 12,728 of 

 Oeltzen's Argelander, a star observed 185 1, April 24, and 

 noted of the eighth magnitude. For i876'o its place is in 

 R.A. i3h. 7m. 325., and N.P.D. 105° 53'7. 



Approximate mean places for 1797, March i, of several 

 stars with which Olbers compared the one in question 

 were : — 



Olbers' Magnitude. R.A. N.P.D. 



{c) 9 194 40 106 6 



{a) 7 194 44 105 24 



[d) II 196 15 105 II 



The star (c) is Lalande 24.421, called by him 8^ ; {d) is 

 L. 24,597, noted 9 ; but the star {a) is not found either 

 in Lalande or Argelander. Its position in Olbers' diagram 

 corresponds to the place above assigned. What is its 

 present magnitude, or is there some mistake about its 

 position ? 



On April i, 1796, the supposed variable was consider- 

 ably brighter than the star («), according to Olbers ; in 

 March 1797, much fainter than {q and only slightly 

 brighter than {d) ; he remarked no change in March, 

 April, and May. Bode says, on April 24 and May 12 

 and 20 of the same year he saw it as a 9'io. In March 

 1855 it was fully eighth magnitude or 77. 



The April Meteors. — As the moon will be absent 

 during the nights of the 19th and 20th of the present 

 month, a watch may be advantageously kept for meteors 

 which are supposed to move in the path of the first comet 

 of 1 86 1 discovered by Mr. Thatcher, of New York, on 

 April 4. At the descending node this comet makes a 

 remarkably close approach to the earth's annual track, 

 the definitive orbit calculated by Prof. Oppolzer, showing 

 that at this point the distance between the two orbits is 

 only 0*00232 of the earth's mean distance from the sun, 

 or 214,000 miles ; less, therefore, than the moon's mean 

 distance from the earth. The elements are elliptical with 

 a revolution of 415 years, and this form of orbit we may 

 assume with much probability to have been occasioned 

 by a near approach of the comet to the earth at some 

 distant epoch. The descending node is passed 22i days 

 before perihelion passage, and to bring the comet into 

 closest possible proximity to our globe, it is necessary 

 that the perihelion point should be passed on May 12. 

 Had this been the case in 1861, the comet would have 

 occupied the following positions on its descent^towards 

 the plane of the echptic : — 



R.A. N.P.D. Distance 



o o frofn earth. 



March 240 ... 269'2 57*4 0700 



April fo ... 270*3 57-0 0*494 



9*0 ... 2713 571 0*281 



„ 17*0 ... 285*2 59*4 0065 



The true dimensions of the orbit of this comet will be 

 defined by the following numbers, which are in units of 

 the earth's mean distance from the sun. 



PROF. HUXLEY'S LECTURES ON THE EVI- 

 DENCE AS TO THE ORIGIN OF EXISTING 

 VERTEBRATE ANIMALS^ 



IV. 



'T^HE crocodiles form the highest group of existing 

 -»- reptiles ; they are higher than lizards as a steam- 

 vessel is higher than a sailing-ship ; for, while built essen- 

 tially on the same lines, and exhibiting altogether the 

 same fundamental structure, they are in some respects 

 peculiarly modified, and that always in the direction of 

 greater complexity. 



Besides the characters of the skull mentioned in the 

 last lecture, they are distinguished from lizards by having 

 a four-chambered heart, one in which the separation of 

 the ventricle into two distinct cavities is completed, so 

 that, in the heart itself, the blood from the lungs is kept 

 separate from that returned from the body generally. A 

 mixture, however, takes place subsequently, through an 

 aperture between the two aortae, one of which spring? 

 from each ventricle. 



Crocodiles are found in Central America, India, Africa, 

 and Australia. Of the many species, the greater number 

 are short-snouted ; the fish-eating Gavial of the Ganges, 

 on the other hand, has an extremely long and narrow 

 snout. 



All the existing crocodiles are fresh-water or estuarine 

 animals, but, fortimately, this was not the case with the 

 ancient forms, many of which were exclusively marine, 

 seeming, so to say, to take the place, in the sea of their 

 own epoch, of our porpoises and dolphins. 



Besides Tertiarj' species, crocodiles are found in the 

 Chalk, Oolite, Lias, and Trias often in the best possible 

 state of preservation ; they therefore extend back to the 

 very commencement of the Mesozoic epoch. 



I A course of six lectuus to workins men, delivered in the thaatr* e< the 

 Royal School of Mines. Lecture IV., March 20. Continued bora p. 430. 



