May 



891] 



NATURE 



69 



sees no reason why it should not be accepted. Making use of 

 Dulong and Petit's generalization and multiplying this number 

 by 138, a normal atomic heat of 6*i8 is arrived at, whereas if 

 multiplied by 180 the abnormal value 8 '07 is obtained. Again, 

 an element of atomic weight i8o should possess a density of 

 8 '2, whereas that of lanthanum is only 6 "48, a specific gravity 

 corresponding to an atomic weight of 138. Considering there- 

 fore the position of lanthanum in the trivalent boron vertical group 

 assured, Dr. Brauner brings forward a redetermination of its 

 atomic weight of his own in order to decide between 138*5 and 

 135. His experimental method consisted in converting known ' 

 weights of the oxide into sulphate. The material employed was 

 obtained by a lengthy process of fractionation with ammonium 

 nitrate, the oxide eventually obtained containing the most positive 

 of the cerite earths (lanthanum oxide) and showing no traces in 

 the spectrum of any others. His value thus obtained is 138 '2, 

 a number closely agreeing with those of Cleve and Bettendorflf. 

 The earlier and lower values of Rammelsberg and others are 

 shown to be probably due to the presence of yttria, which was 

 not detected by these observers, inasmuch as the work of Thalen 

 and Bunsen upon the spectrum of yttrium had not then been 

 published. Hence lanthanum of atomic weight 138*2 retains | 

 the place in the trivalent group of the periodic system marked ; 

 out for it by its well-known basic properties. j 



The additions to the Zoological Society's Gardens during the 

 past week include a Striped Hyaena {Hyana striata ? ) from 

 India, presented by Mr. B. T. Ffinch, C.M.Z.S. ; two Hairy - 

 lumped Agoutis {Dasyprocta prymriolopha) from British Guiana, 

 presented by Mr. H. Barrington ; two Brent Geese {Bernicla 

 brenta), a Pintail {Dafila acuta i ), two Wigeons [Mareca 

 Penelope <J 9 ), a Common Sheldrake (Tadorna vulpanser ? ), 

 two Golden Tench {Tinea vulgaris, van), nine Golden Carp 

 (Carassius auratus), British, presented by Mrs. Atkinson ; eight 

 European Tree Frogs {Hyla arbor ea) from the South of France, 

 presented by Mr. Clifford D. Fothergill ; a Crested Porcupine 

 {Hystrix cristata) from India, a Tibetan Crossoptilon {Crossop- 

 tilon tibetanum ? ) from Western China, deposited ; two Swin- 

 hoe's Pheasants {Euplocamus swinhoii S ? ) from Formosa, two 

 Japanese Pheasants (Phasianus versicolor 9 9 ) from Japan, two 

 Amherst's Pheasants ( Thaumalea amherstid 9 9 ) from Szechuen, 

 China, a Black-necked Stilt Plover [Himantopus nigricollis), a 

 Cayenne Lapwing ( Vanellus cayennensis) from South America, 

 purchased ; a Wild Swine {Sus scrofa 9 ) from Persia, received 

 in exchange ; two Indian Desert Foxes (Canis leucopus), born 

 in the Gardens. 



OUR ASTRONOMICAL COLUMN. 



The Photography of Faint Nebulae.— In the Journal 

 of the British Astronomical Association for February, Dr. Max 

 Wolf, of Heidelberg Observatory, contributes a note on a 

 nebula surrounding f Orionis, the third star in the belt, which 

 he has discovered on photographs taken with a 4-inch portrait 

 lens. Some reproductions submitted to the Association show a 

 large amount of nebulosity south-west of ^, also nebulous ground 

 around f, and a nebulous star north of i. Dr. Wolf's note is 

 important, inasmuch as it indicates that the 4-inch portrait lens 

 used at Heidelberg gives results which compare favourably with 

 those obtained at Harvard with a much larger instrument, viz. the 

 Bache equatorial of 8 inches aperture and 44 inches focal 

 length. With regard to the use of portrait lenses for celestial 

 photography, Dr. Wolf makes a few succinct remarks. In 

 photographing the stars, the intensity of the image depends only 

 upon the area of the lens employed, and an instrument of 

 20 inches diameter therefore requires 25 times less ex- 

 posure than one 4 inches in diameter having the same 

 focal length, in order to obtain the same number of stellar 

 images. But it is a different thing with comets, nebulae, and 



the like— bodies having a finite area. The intensity of the 



image at the focus then varies as the fraction (A- V, where d is 



the diameter of the object-glass, and / its focal length. If, 

 therefore, the intensity of the light received with an aperture of 

 20 inches and focal length of 100 inches be expressed by 0*04, 

 that of a portrait lens of 4 inches aperture and 12 inches focus 

 iso'ii. This shows that in order to photograph the same faint 

 nebula, the instrument of 20 inches aperture requires an ex- 

 posure about three times as long as the 4-inch portrait lens. 



Another paper having the same purport is contributed by Dr. 

 Hoidentovol. iii. No. 14, of the Publications of the Astronomical 

 Society of the Pacific, from which it appears that from 80 to 100 

 minutes' exposure with the 33-inch Lick telescope will give 

 about the same number of stars as 205 minutes' exposure with 

 Mr. Roberts's 20-inch reflector. When, however, the amount of 

 nebulosity depicted is considered, the advantage is considerably 

 in favour of the short-focus reflector, a comparison of the results 

 obtained with the two instruments indicating that 15 minutes* 

 exposure with the reflector is about as effective in showing the 

 nebulosity of Orion as 60 minutes' with the refractor. 



Variations in Latitude.— Prof. H. G. van de Sande 

 Bakhuyzen extends our knowledge of this subject in a paper 

 contained in the March number of the Monthly Notices of 

 the Royal Astronomical Society. The conclusions deduced 

 from the investigation of observations of Polaris made be- 

 tween 185 1 and 1882, and the interesting researches of Mr. 

 Thackeray (Memoirs R.A.S., vol. xlix. p. 239), may be 

 summed up as follows:— (i) The monthly discordances in 

 the zenith distances of Polaris are, for the greater part, 

 not caused by a real variation of latitude, but chiefly by an 

 effect of temperature. (2) It is not possible to explain those 

 discordances by an error in the indications of the exterior ther- 

 mometer, or by an influence depending only on the exterior 

 temperature. (3) The discordances can be explained, for the 

 greater part, by a cause depending on the difference of the 

 exterior and interior temperatures. (4) Probably that cause is 

 a refraction in the observing-room, and its effects are sensibly 

 proportional to those differences of temperature. (5) The dis- 

 cordances corrected for that refraction are about the same for 

 both culminations, and can be explained by a real variation of 

 latitude. 



An investigation of the mean North Polar distances of Polaris 

 in both culminations observed at Greenwich between 1883 and 

 1889 leads to the conclusions : (i) that it is probable that the 

 observations of Polaris at Greenwich confirm the variations of 

 latitude observed elsewhere in 1884-1885 and 1889-1890 ; (2) 

 that there is a very strong probability that the variations in these 

 years had an exceptional character, and do not agree with the 

 annual variations, deduced from the observations of Polaris at 

 Greenwich during the period 1851-1882. 



Re-discovery of Wolf's Comet (1884 \\\.).—Astro- 

 nomische Nachrichten, No. 3033, contains the information that 

 Wolf's periodical comet was observed on its return by Prof. 

 Barnard, of Lick Observatory, on May 3*9792 G.M.T. The 

 following ephemeris is from one given in Edinburgh Circular 

 No. 15, by Prof. Berberich. The brightness of the comet at 

 re-discovery has been taken as unity. 



Ephemeris for Berlin Midnight. 



NO. I 125, VOL. 44] 



The comet will pass perihelion on September 3*3199 Berlin 

 mean time. It is near a Pegasi at the present time, and may 

 therefore be seen just before sunrise. The motion is towards 

 Andromeda. 



