1 42 Miscellan eons Intelligen ce. 



When taken from the camera the proof is to be placed upon a plate 

 of glass or porcelain, which has been slightly moistened in order that 

 the paper may adhere to it. A saturated solution of gallic acid being 

 poured over the proof, the image appears at once. The acid is allowed 

 to act until all the details are brought out, but not until the white por- 

 tions are discolored ; to prevent this, the acid is removed by pouring 

 a large quantity of pure water over the proof, which is finally entirely 

 covered by a solution of 1 part bromid of potassium in 40 pts. distilled 

 water. The paper remains in this last solution for a quarter of an hour, 

 and is then well washed with clean water and dried between sheets of 



filtering paper. To render this negative impression more transparent, 



for the purpose of copying, a little wax may be scraped upon it and 



melted by a hot smoothing iron, some sheets of letter paper being 

 placed between. 



The paper for the positive proof should be very stout and as smooth 

 as possible. Prepare a solution of 3 parts water saturated with com- 

 mon salt and 10 pts. distilled water ; upon this float the paper for two or 

 three minutes, and then dry it as much as possible by absorbent paper; 

 and next float it upon a solution of 1 part nit. silver and 5 pts. water, 

 until another sheet having undergone the previous process is ready to 

 take its place ; it is then to be removed, drained, and dried as before 

 directed. In this way a quantity may be prepared in a short time. 

 The positive paper is to be preserved in the way directed for the other, 

 but must not be kept more than one or two weeks, or it will lose its 

 delicacy and become discolored. 



The positive proof is made by the usual process, the expose being 

 as far as possible to the direct sunlight ; about twenty minutes being 

 the average time. 



To fix this proof, it is to be taken into a darkened apartment, soaked 

 for fifteen minutes in pure water, and then put into a solution of 1 p*rt 

 hyposulphate of soda and 8 pts. distilled water. It may now be ex- 

 amined by daylight, and the action of the hyposulphate watched. 

 Gradually the lights become more brilliant, and the shades pass from a 

 dirty red to a bistre and finally come to resemble those of an aquatint. 

 When the desired tint is reached, the operation is stopped and the salt, 

 removed by soaking in water for five or six hours to a whole day 



Several proofs can be immersed at the same time in the hyposulphate, 

 and those which do not stand its action for two hours must be rejected. 

 The operations although in appearance complicated, are in reality qu» te 

 simple and of easy execution. G. C. S. 



7. Report on the Aurora Borealis. — Aurores Boreales, 1 vol.,8vo. 

 Accorripagne d'un Atlas de 12 planches in folio ; par MM. Lottie 

 Bravais, Lillijshook, et Siljestrom.* 



The following notice of this great work is from M. Bravais. He re- 

 marks; — 



I have divided my general review of the subject into eight paragraph 



In the first, I examine the much controverted question, as to the nature 



^l , . B ,.°, ne of a 8erles of twenl y- s ix volumes of large 8vo, and seven toi\ 



S €S,P « S ^ eda9ther 7 l,ltS ° f " Vo y fl ges de la Commission Scientifiq** * 

 ^ora, en fccandinavie, en Lapome, au Spitzburg et aux Feroe, pendant fefl aniieea 





