6q6 PHILOSOPHICAL TRANSACTIONS. [ANNO 1785. 



what I figuratively called the laboratories of the universe, the stars forming these 

 extraordinary nebula;, by some decay or waste of nature, being no longer fit for 

 their former purposes, and having their projectile forces, if any such they had, 

 retarded in each other's atmosphere, may rush at last together, and either in 

 succession, or by one general tremendous shock, unite into a new body. Per- 

 haps the extraordinary and sudden blaze of a new star in Cassiopea's chair, in 

 1572, might possibly be of such a nature. But lest I should be led too far 

 from the path of observation, to which I am resolved to limit myself, I shall 

 only point out a considerable use that may be made of these curious bodies. If 

 a little attention should prove that, having no annual parallax, they belong most 

 probably to the class of nebulas, they may then be expected to keep their situa- 

 tion better than any one of the stars belonging to our system, on account of 

 their being probably at a very great distance. Now to have a fixed point some- 

 where in the heavens, to which the motions of the rest may be referred, is 

 certainly of considerable consequence in astronomy ; and both these bodies are 

 bright and small enough to answer that end*. W. Hekschel. 



Datc/iet, near Windsor, January 1, 1785. 



XIII. Remarks on Specific Gravities taken at Different Degrees of Heat, and an 

 Easy Method of Reducing them to a Common Standard. By Rich. Kirwan, 

 Esq., F.R.S. p. 267. 



One capital advantage derivable from a table of specific gravities, is the know- 

 ledge of the absolute weight of any solid measure of the substances, or that of 

 the solid measure of a given weight of those substances, a cubic foot of water 

 being supposed to weigh 1000 oz. avoirdupois, and consequently a cubic inch of 

 water weighing 253.182 grs. But all those who have treated this subject, have 

 neglected to inform us of the temperature at which this agreement takes place ; 

 yet that it cannot take place in all temperatures is evident from the experiments of 

 Dr. Halley and others, who have found, that from a few degrees above the 



* Having found two more of these curious objects, I add die place of them here, in hopes that 

 those who have fixed instruments may be induced to take an early opportunity of observing them 

 carefully. 



Feb. 1, 1785. A very bright planetary nebula, about half a minute in diameter, but the edges 

 not very well defined. It is perfectly round, or perhaps a very little elliptical, and all over of a 

 uniform brightness : with higher powers it becomes proportionally magnified. It follows y Eridani 

 l6 m 1(»' in time, and is 49' more north than that star. 



Feb. 7, 1785. A beautiful, very brilliant globe of light ; a little hazy on the edges, but the hazi- 

 ness goes off very suddenly, so as not to exceed the 50th part of the diameter, which I suppose to 

 be from 30 to 40". It is round, or perhaps a very little elliptical, and all over of a uniform bright- 

 ness : 1 suppose the intensity of its light to be equal to that of a star of the <)th magnitude. It pre- 

 cedes the third b (Kl. (.) Crateris 28 m 36' in time, and is 1° 25' more north than that star. — Orig. 



