326 



NATURE 



[February 2, 1893 



from the Argentine Republic, presented by Mr. Hill ; a Rough 

 Terrapin {Clemmys punctularia)hom Guiana, presented by Mr. 

 J. J. Quelch, C.M.Z.S. ; an American Milk Snake {Coluber 

 eximius) from Tennessee, presented by Miss Winifred M. 

 Middleton ; a Virginian Eagle Owl {Bubo maximus) from South 

 America, deposited ; two Mouflons {Orlis musimon, <J 9) from 

 Corsica, received in exchange. 



OUR ASTRONOMICAL COLUMN. 

 The Nautical Almanac for 1896. — The new superin- 

 tendent of the Nautical Almanac office has introduced a much- 

 needed reform into the first almanac, that for 1896, issued under 

 his direction. The state of the British Nautical Almanac has 

 long been severely criticised as being far from the best possible 

 for navigational purposes both in form and contents, and by no 

 means satisfactory from the astronomical standpoint. A letter 

 addressed by the Shipmasters' Society to Dr. Hind, the late 

 Superintendent, in November 1891, pointed out the advantage 

 to navigators which would be offered by a work published at a 

 popular price, and without that astronomical information which 

 is of no use to sailors. Many low-priced almanacs are published, 

 indistinctly printed, and having occasional errors in the figures, 

 and an official trustworthy book was very desirable. In conse- 

 quence of this representation the almanac is now published in two 

 forms — as the complete almanac of former years, price 2.s. 6d. ; 

 and as Part I. of the Nautical Almanac, specially suited for the 

 use of sailors, price \s. 



The complete almanac has been revised and added to, many 

 of the recommendations of the Nautical Almanac Committee 

 of the Royal Astronomical Society, which reported to the 

 Admiralty in 189 1, having been adopted. The small short 

 period terms of nutation have been tabulated, and, correspond- 

 ing to that, additional day numbers are added so as to enable 

 computers to include those small terms in the star corrections. 

 The catalogue of stars from which the moon culminators artd stars 

 occulted by the moon are obtained has been revised and en- 

 larged, and the mean places of the stars of this catalogue, which 

 are used during the year, are also included. The elements of 

 the occultations are given in a revised form similar to that 

 adopted in most of the other astronomical ephemcrides, so that 

 the circumstances of an occultation for any position on the 

 earth's surface can be computed with facility. There has been 

 a general revision of the constants used. 



The small almanac has been arranged by Mr. Downing in 

 conference with the Hydrographer. As the guiding principle in 

 publishing this was the minimum of change in the parts of the 

 almanac which were to be extracted and published separately, 

 there is still much in the volume that is not needed by sailors, 

 but the omission of which would have necessitated the setting 

 up of fresh type and much extra work at the Nautical Almanac 

 office. The monthly part is printed unaltered, and consequently 

 contains the sun's and moon's latitude and longitude, which are 

 not required by sailors. The noon ephemerides for the brighter 

 planets, Venus, Mars, Jupiter, and Saturn ; the catalogue of 

 mean places of stars, as well as the apparent places of the nine 

 stars used for lunar distances ; the eclipse section and the tables 

 for navigation are then given. There is no doubt that the issue 

 of this smaller work will confer a real benefit on the shipping 

 community, and that it will soon win its way to popularity. 



In announcing these changes to the Royal Astronomical 

 Society, Mr. Downing expressed the hope of being able, through 

 the economy of time effected by international co-operation in 

 some of the work of the office, to make considerable future 

 additions to the almanac without increasing the burden of the 

 British taxpayer. The duplicate work done at Berlin, London, 

 Paris, and Washington involves much waste of energy which 

 might be more usefully expended : and as a step towards this, 

 Mr. Downing, last summer, arranged with Prof. Newcomb, of 

 Washington, to co-operate in some of the work of their re- 

 spective almanacs, and the Admiralty have consented to this. 

 It is to be hoped, in the interests of astronomy and of navigation, 

 that the scheme may be greatly extended. 



Eclipse Photography. — The results obtained by M. de la 

 Baume Pluvinel at Salut Isles in 1889 (as given in his lecture 

 which appeared in Nature last week), when he photographed 

 the corona with photographic actions varying from 185 to 13, 

 and found the photographic action of -30 the most satisfactory; 



NO. I 2 14, VOL. 47] 



do not agree with those of the English expedition obtained at 

 the same time and place. The photographic actions on the 

 plates exposed with the 20-inch mirror of 45-inches focus, by the 

 late Father Perry, varied from 1975 to 790* as calculated by 

 the formula given by M. de la Baume Pluvinel, and in every 

 case increase of photographic action gave greater extension of 

 the corona. Mr. Rooney's plates, with the 4-inch lens of 61 

 inches focus, had been subjected to photographic actions varying 

 from i"ii to I77'77, and agreed with Father Perry's in giving 

 greater extension with every increase of photographic action. 

 The English results certainly justify the conclusion that greater 

 photographic action is necessary to photograph those faint 

 extensions of the corona which have been seen, but have 

 hitherto eluded attempts to photograph them. 



Mr. Burnham's experiments, alluded to by M. Pluvinel, do 

 not assist us in this question. A certain absolute amount of 

 light is necessary to give any appreciable photographic effect on 

 the plate, and this seems to be the chief difficulty in obtaining, 

 photographs of the external corona. In Mr. Burnham's 

 experiments he had too much light and had to cut down the 

 exposure in order to get faint contrasts, but there was never any 

 question of not having sufficient light to obtain any photographic 

 effect. Captain Abney finds (Phil. Trans, vol. cixxx. A, page 

 314) that an abrupt change of \ per cent, in the intensity of light 

 can be detected on a photograph, hence we may look upon a 

 negative as a drawing built up of 200 different shades. Over 

 exposure will of course prevent such faint contrasts as \ per cent, 

 being detected, and under exposure will enable fainter con- 

 trasts to be seen, so long as the limit of minimum exposure 

 necessary to produce any photographic effect is passed; but the 

 evidence from the English expedition renders it extremely 

 probable that even with the largest photographic action used 

 this limit was not actually reached with the faintest extensions 

 of the corona. 



Comet Holmes.— Dr. F. Cohn, writing about this comet 

 from the Observatory in Konigsberg on January 17, finds 

 (Astronomische Nachrichten, No. 3146), with a 6-inch heliometer 

 and a magnification of 65 times, that the nucleus is exactly as a 

 star of the 8th magnitude. The correction to the ephemeris given 

 below is, as he has deduced, Aa = - 0'3s., A5 = - 6". 



Dr. R. Schorr, of the Hamburg Observatory, puts the nucleus 

 down on the same date as a 7*2 magnitude star with a small 

 nebulosity about it of 5" diameter, but on the 18th he found the 

 comet showed a much larger coma, a measurement giving 87". 

 The stellar nucleus was also estimated as 7 '5 magnitude of 

 a diameter 2". 



The ephemeris of this comet is from Prof. Schulhof's calcula- 

 tions {Astronomische Nachrichten, No. 3140) : — 



1893. 

 Feb. 2 

 3 

 4 

 5 

 6 



7 



R.A. app. 

 h. m. s. 



I 45 46-5 ••• 



47 i6-6 ... 



48 47'3 ••• 

 50 i8-6 ... 



'51 50-4 ■•• 



53 22-8 ... 



54 55-8 ... 

 I 56 293 ... 



Decl. app. 



+ 33 49 26 

 50 48 



52 14 



53 45 



55 20 



56 59 

 58 41 



34 o 28 



Comet Brooks (November 19, 1892). — The following i^ 

 an ephemeris for Comet Brooks for the ensuing week : — 



1893. R.A. app. Decl. app. Log r. Log A. Br. 



h. m. s. 01 



Feb. 2 ... 23 56 48 ... -f34 277 



3 ••• 23 59 13 ••• 33 44'4 ••• 01050 ... 0-1295 ... 1-90 



4 ... o I 31 ... 33 3*3 



5 ... 3 42 ■. 32 24-1 ... 0-1087 ... 0-1482 ... 1*71 



6 ... 5 48 ... 31 46-4 



7 ... 7 48 ... 31 10-4 

 8... 9 43 •.. 30 35'8 



9 ... o II 33 ... 30 29 ... 0-1167 ••■ 0-1832 ... 1-40 



The Andromedes. — Although Mr. Maclair Boraston was 

 unfortunate in having bad weather on the nights of November 

 13 and 14 last, thus obscuring the Leonids, yet the magnificent 

 shower of the Andromedes that he describes in Astronomy and 

 Astrophysics for January should have recompensed him some- 

 what for "the great elevation of the radiant point, combined 

 with a cloudless tropical sky, the absence of moonlight and the 

 unobstructed view of the complete hemisphere, afforded the ne 

 plus ultra of astronomical requirement." Observing ia 



