586' PHILOSOPHICAL TRANSACTIONS. [anNO l/SQ. 



mixtures made of marine acid with vitriolated natron, muriated ammonia, and 

 nitrated kali, in the proportions mentioned above, this being much cheaper than 

 those made with diluted nitrous acid, and very nearly equal in effect. In his 

 last paper Mr. W. mentioned a freezing mixture, made by dissolving a powder 

 composed of equal parts of muriated ammonia and nitrated kali in water, and 

 therein directed 6 parts of the mixed powder to be added to 8 parts of water ; 

 but he has found since, that the best proportions are, 5 parts of the former to 

 8 of the latter, by which he has sunk the thermometer from 50° to 1 1°. 



Having now prosecuted his subject relative to mixtures for generating artificial 

 cold without the use of ice, from a possible method proposed by Dr. Watson 

 (Essays, vol. 3, p. 139,) foi" freezing water in summer in this climate, and car- 

 ried it on to a certain method of freezing, not only water, but even mercury, 

 in the hottest climate, Mr. W. takes his leave of it. 



XX. Catalogue of a Second Thousand of New Nebula and Clusters of Stars ; 



with a few Introductory Remarks on the Construction of the Heavens. By 



Wm. Herscheh LL. D, F. R. S. p. 212. 



By the continuation of a review of the heavens with a 20 feet reflector. Dr. 

 H. was now furnished with a 2d 1000 of new nebulae. The form of this work 

 is exactly that of the former part, the classes and numbers being continued, and 

 the same letters used to express, in the shortest way, as many essential features 

 of the objects as could possibly be crowded into so small a compass as that to 

 which I thought it expedient to limit myself. The method I have taken of ana- 

 lyzing the heavens, as it were, is perhaps the only one by which we can arrive 

 at a knowledge of their construction. In the prosecution of so extensive an 

 undertaking, it may well be supposed that many things must have been sug- 

 gested, by the great variety in the order, the size, and the compression of the 

 stars, as they presented themselves to my view, which it will not be improper to 

 communicate. 



To begin our investigation according to some order, let us depart from the 

 objects immediately around us to the most remote that our telescopes, of the 

 greatest power to penetrate into space, can reach. We shall touch but slightly 

 on things that have already been remarked. From the earth, considered as a 

 planet, and the moon as its satellite, we pass through the region of the rest of 

 the planets, and their satellites. The similarity between all these bodies is suf- 

 ficiently striking to allow us to comprehend them under one general definition, 

 of bodies not luminous in themselves, revolving round the sun. The great di- 

 minution of light, when reflected from such bodies, especially when they are 

 also at a great distance from the light which illuminates them, precludes all pos- 

 sibility of following them a great way into space. But if we did not know that 



