Magntf ism. — Heal ofFacuuyn. — Fine Ails. 22!) 



tain quantity of the subacetate. The silk thus prepared is after- 

 wards immersed in a weak solution of chromate of potash, which 

 causes it to assume a yellow colour, which continues to deepen 

 more and more for about ten minutes, when it reaches its greatest 

 intensity. The silk is then washed and dried. 



A solution of native chromate of iron, decomposed by nitrate 

 of potash, and saturated with nitric aeid, may be employed in 

 place of the neutral chromate of potash. 



This colour is unalterable in the air ; and by varying the pro- 

 portions of subacetate of lead, and the chromate of potash, tints 

 varying from pale to deep yellow may be obtained. 



The process is applicable also to woollen, cotton, and linen • 

 but with these the solution of subacetate should be heated to 

 about 130'' of Fahrenheit. 



This dye however is liable to the inconvenience of being par- 

 tially decomposed by soap : its use therefore had best be confined 

 to silk. 



MAGNETISM. 



Professor Hansteen, of Christiana, has announced that he has 

 ascertained that every perpendicular object, of whatever mate- 

 rials, — for instance, a tree, the wall of a house, &c., — has a mag- 

 netic north pole at the foot, and a south pole at the top. An- 

 nals of Philosophy, N, S. No. 2. 



HEAT OF VACUUM. 



M. Gay Lussac has lately proved by well contrived experi- 

 ments, that when any portion of space, void of ponderable mat- 

 ter, is suddenly dilated or diminished, a thermometer, in such 

 space, undergoes no sensible change. It appears plainly, that a 

 vacuum, if it contain caloric at all, cannot contain it in the way 

 that bodies do ; and that the heat which irradiates through it 

 instantaneously, is all that it holds, and is so infinitely small as 

 not to be appretiable by instruments. 



FINE ARTS. 



We have great pleasure in announcing that a desideratum long 

 called for has at length been gained, for giving to the public 

 suitable convenience for viewing in a proper manner the produc- 

 tions of our engravers. It is now determined to open a regular 

 exhibition of engravings of living British artists; and as the 

 King has most graciously given the undertaking his Royal pa- 

 tronage, there can be no doubt of its success. The exhibition 

 will open in the middle of April, under the direction of a super- 

 intending committee of engravers. 



The very high state of perfection to which the art of engraving 

 has been brought in (ircat Britain, and the inettcctive modes in 



which 



