late D'lfcover'ies in Scicvcr. i.T^ 



^efccndincr node,- 3 figns 9° 34' : pl^ce of the perlhclioa in 

 the orbit, 3° 36': inclination of the orbit, 50^ 52'; : direcr 

 lion of its movement, retrograde: patl^ige at the penhelion 

 ontheaiftofFruaidor, yeary, (Sept. 7, 1799O at 4 hcurs 

 34 minutes mean time at Paris : diUance of the perihehon 

 0-8^387.— This is the tenth comet difcovered by Mochain. 



LUMINOUS FLUID. 



Fabbroni has examined the refraftive po^vcr of various 

 iiuids, and (hown that they are exceedingly different. Thu?, 

 tether has a refradive power much more confiderable than 

 oil The former gives a focus of 60, the latter of 75. 



Haiiy has (hown that feveral mineral fubftances have a • 

 double refraaion ; fuch as, tranfparent quartz, the topas, the 

 emerald, calcareous fpar, lulphat of barytes, the euclafe the 

 idocrafe, fulphat of ftrontian. Among the foluble and fapid 

 falts, borat of foda (borax) and fulphated magncfia have 

 double refraaion ; fulphur has double refraction ; amber and 

 the diamond have fmgle refraaion; caibonat of lead, or 

 white lead ore, has double refraaion. 



Brou<rham, in a paper printed in the Tranfadions of the 

 ^oval S'ociety, civcs an account of fome experiments whuh 

 feem to him to prove that the dodrine of Newton refpeamg 

 the refrangibilitv of the rays of light, is falfe. Prevolt, of 

 Geneva, thinks' that Brousham is miftaken : he mamtams 

 the theory of Newton, and Ihows that the expf.riracnts op- 

 pofed to it are not conclufive. ^ 



Dize has confidered the matter of heat as the caule of all 

 luminous eflVas. He has made a great number of experi- 

 ments to prove, thafin all the terrefbial phenomena there is 

 never licrht without heat. His conclufions are : 1 . That heat 

 always precedes luminous cfleas. %. That light cannot be 

 a body fmg^ru-rh; bccaufe light does not take place but 

 when caloric is free, and in fufficient accumulation, on which 

 depends the force of the luminous effea produced. 3. i he 

 effea called luminous can only be a luminous property, 

 which every molecula of free caloric poflefles. 4. Caloric 

 being a fubftance, the quantity of which is limited, darts 

 itftlf lo-.vards the fun, which is its llrongell point of attrac- 

 S a tion. 



