ON THE NATURE OF THE SON- 21 . 



IN a fubfequent paper of the fame volume, Dr. Herfchel Subfequent ob- 

 gives a number of additional obfervations, made in the fprfrig ervatlons * 

 of 1801, by which it appears that the fun continues to ex- 

 hibit fymptoms of a plentiful emiffion of light. He ftrongly Sufpicion that 

 fu fpeds that one half of our fun is lefs luminous than the ^{^"ndaa 

 other, and that its variable luftre may poflibly appear to other obfcurc fide, 

 folar fyftems as irregular periodical liars are feen by us ; bu fc 

 whether this arifes from fome permanent conftru&ion of the 

 folar furface, or be merely an accidental circumftance, mull 

 be left to future inveftigation. 



He takes notice that we need not in future be at a lofs Judgment of the 

 with regard to the current temperature of this climate, as m o m "trical re- 

 the thermometrical obfervations, regularly given in the Phi- gifters. 

 lofophicai Tranfactions, afford a proper ftandard of com- 

 parifon with the folar phenomena. • 



In this paper alfo, with a drawing, is defcribed a method Very advantage- 

 of fubftituting liquids inftead of dark glafles, for moderating j^e-Jof the' 

 the folar light and heat m telefcopes. It is a fquare trough, dark glafles of 

 clofed at two oppofite ends by well polifhed parallel plane; tele pes * 

 glafles. On one fide of this trough is a fmall handle, and on 

 the other a lip or fpout for pouring out any portion of the 

 liquid when the reft is to be diluted. The trough is made to Apparatus, 

 fit into an excavation in the eye tube of the telefcope, and in 

 this fituation the folar rays muft pafs through the liquid 

 therein contained before they arrive at the eye. By colouring 

 the fluid, the obferver has it in his power to foften the light 

 at pleafure ; and water keeps off the heat fo as to prevent 

 the leaft inconvenience. It is eafy to make trial of a variety 

 of fluids in this way. Among other mixtures, the Do6lor 

 found that ink, diluted with water, and filtered through 

 paper, fliewed the folar image as white as fnow, and very 

 diftinft. Through this mixture he could obferve the fun in 

 the meridian for any length of time without danger to the eye, 

 or to the glafles, with a mirror of nine inches in diameter, 

 and the eye-pieces open, as they are ufed for night obfer- 

 vations, 



IV.— Ob. 



