196 MATHEMATICS AND NATURAL PHILOSOPHY. 



We presume that the picture may be fixed either with hyposulphite of soda, 01 

 with cyanide of potassium. 



These plates may be used the day after they have been finally sensitized. After 

 the operations I. and II. have been performed the plate is apparently insensible 

 to the action of light; one experiment mentioned in the Bulletin seems to contra- 

 diet this, but we strongly suspect that the sentence must be wrongly printed. 

 The following details of the operation may be also useful. It seems that the 

 same aceto-nitrate bath mentioned in III. may be used for exciting the collodion 

 film in I. Tbe collodion itself must be very thin, or blisters are apt to be formed- 

 The directions given in the Bulletin are rather vague; but we should imagine that 

 a collodion containing from 1 to \\ grains of gun-cotton per ounce would be suit- 

 able. The proper consistence of the collodion, however, seems to depend upon 

 that of the albumen. M. Taupenot appears to use pure albumen, without adding 

 water, but after fermentation. To the white of egg he adds about 10 per cent, of 

 honey, and a small portion of yeast. The advantages of thus fermenting the 

 albumen are, that beating is rendered unnecessary, and that the albumen will 

 keep. He then adds l-h per cent, of iodide of potassium. As a rough guide to 

 the quantity thus indicated, we may notice that according to M. Negretti's esti- 

 mate this will give about 7 grains of iodide of potassium to the white of a large 

 egg. The following suggestion with regard to the development, from the pen of 

 an experienced photographer (Mr. Sutton) is likely to be useful : — 



" Take two glasses, into one pour the usual pyro-gallic solution, and into the 

 other some diluted aceto-nitrate. Before developing moisten the plate with water, 

 then pour on the pyro ; no effect will be perceived at first ; let it remain a minute 

 or two, then pour off into the glass, and pour on the dilute aceto-nitrate. The 

 development will now begin, and will advance rapidly. When the picture is 

 nearly out pour off the aceto-nitrate, and pour on the pyro-gallic, and proceed in 

 this way by changing the solutions (but never mixing them) until the end. 



G. C. I. 



VARIABLE STARS. 



The following communications from Mr. J. R. Hind, which have recently 

 appeared in the London Times, it will be seen are possessed of considerable inte- 

 rest to the scientific astronomer ; they were both published in the form of letters, 

 dated from Mr. Bishop's Observatory, Regent's Park, London, where Mr. Hind's 

 observations are carried on ; the first of these being dated on the 18th, and the 

 gecond on the 21st of December last : — 



NEW VARIABLE STAR OR SMALL PLANET. 



About 9 o'clock on Saturday evening I remarked, near 84 Geminorum, an object 

 shining as a star of the ninth magnitude, which I have not seen before during the 

 five years that my attention has been directed to this part of the heavens. At 5 

 o'clock on the following morning it appeared to be in the same place, whence I 

 conclude it must be a variable star of long period, recently come into view. It is, 

 however, just possible that a small planet hereabouts might have been stationary, 

 and the weather having continued cloudy since my last observation. I am induced 

 to notify the circumstance, that the nature of this object may be ascertained as 

 early as possible. Its mean place for January 1, 1856, is in right ascension 7h 

 46m. 33.65s., and north Polar distance 67° 37' 17.1". It exhibits the pale blue 

 light which characterizes many of the telescopic planets, and nothing of the fiery 

 appearance often presented by variable stars. Still I incline to place it in the 

 latter class. 



