Penetration into Space by Tele/copes. 9 



of oxygen, 43.3 grains of carbonic acid. Now this acid confifts of 8.6 grains of carbone, 

 and 34.6 of oxygen nearly } but the quantity of oxygen employed was only 13.6 grains, 

 hence the difference between 34.6 and 13.6, or 2i grains, muft have been originally con- 

 tained in the gas. It would therefore appear, that the gafeous oxides in their pureft (late 

 confift of oxygen and carbone in the proportion of 21 to 9 nearly, combined with caloric. 

 Woohuich, March 19, 1801. 



II. 



On (he Power of penetrating into Space by Telefcopes ; with a comparative Determination of 

 the Extent 0/ that Power in natural Vifion, and in Telefcopes of various Sizes and Con~ 

 flru£lions-y illuJlratedbyfekB Obfervations. By Wiliiam Herschel, LL, D. F.R.S. 



(Concluded from Vol. IV, page SS4-J 



July 12, 1784. I viewed the fame nebula with a large 20-feet Newtonian refleftor; 

 power 157. 



" A moil beautiful extenfive duller of ftars, of various magnitudes, very compreffed in 

 *' the middle, and about 8' in diameter, befidcs the fcattered ones, which do more than 

 •' fill the extent of the field of view * : the large ftars are red ; the fmall ones are pale red. 

 *'RA i8''23'39"5 PD 114° 7'." 



The penetrating power of the firft inftrument was 39, that of the latter 6 1 ; but, fronv 

 the obfervations, it is plain how much fuperior the effeft of the latter was to that oF the 

 former, notwithftanding the magnifying power was fo much in favour of the inftrument 

 with the fmall penetrating power- 

 July 30, 1783. With a fmall 20-feet Newtonian refleftor, I viewed the nebula in the 

 hand of Serpentarius, difcovered by Mr. Meflier, in 1764. 



" With a power of 200, I fee it confifts of ftars. They are better vifible with 30O. 

 ♦' With 600, they are too obfcure to be diftingulflied, though the appearance of ftars is ftill 

 " preferved. This feems to be one of the moft diflicult objefts to be refolved. With me, 

 " there is not a doubt remaining; but another perfon, in order to form a judgment, ought 

 " previoufly to go through all the feveral gradations of nebulae which I have refolved into 

 « ftars." 



May 25, 1791. I viewed the fame nebula with a 20-feet refle£lor of my conftrudlion. 



V • • ,v/, 64x188^' ^ _ 



having a penetratmg power 01 ■- = 75>o*»' 



* This field, by the pafTage of an equatorial ftar, was i j' 3". 



Vol. v.— April 180 1. C "With 



