M. Be.ssel on the Declination of the Stars. 451 



combustion is imperfect; all the hydrogen is burnt, but not the 

 whole ot" the carbon which was dissolved in it : having lost that 

 which supported it in the form of gas, the carbon becomes vi- 

 sible as a black powder ; and wherever this is seen, it is an in- 

 dication that the consumer has wasted more than he has paid 

 for. 



There is no sulphurous acid generated in the combustion of 

 oil gas, and very little in coal : thus Dr. Henry has shown 

 that gas purified in the ordinary way contains 1-I0,000dth of 

 its volume of sulphuretted hydrogen ; and as a No. 4 burner 

 would at its ordinary rate consume 5500 cubic I'eet in a year, 

 about half a cubic foot of sulphuretted hydrogen would be 

 mixed with it, which would form about Ih oz. of sulphurous 

 acid, too trivial to notice ; in fact, it was scarcely worth the 

 trouble to notice the products of combustion at all, because 

 they may be easily removed by having a conductor over the 

 light. 



4th, There is one propert}^ of oil gas which makes it much 

 less fit for a public light than coal gas, — it is so very easily 

 extinguished. I have repeatedly extinguished with my breath 

 a No. 4 burner at the measured distance of nine feet, and I 

 should think that on windy nights a whole district of it would 

 often be in darkness. 



5th, Relative selling price. Tlie standard selling price of 

 coal gas is, I believe, about 155. per thousand cubic feet, and 

 of oil gas 50^. If the mean densities I have here calculated 

 upon, — "900 oil, "500 coal, — be correct, and I am confident they 

 are not far from the truth, the prices should be, 1 5s. for 

 coal gas, 37s. 6(L for oil gas: all above that sum is excess of 

 charge above value ; consequently oil gas at 50s. per thousand, 

 as usually manufactured, is SS^^Jtv cent, dearer than it should 

 be, according to the light it gives. 



Bristol, ofi Old Market-street, WlI.LlAM Herapath. 



May 20, 1823. 



LXXXVIII. M. Bessel on the Declination cf the Stars* 

 'T^IIE Number of Tilloch's and Taylor's Magazine for F^- 

 ^ bruary 1823, which you kindly forwarded to me, arrived 

 in due course; and from it I have seen with pleasure, that the 

 great difierence betwixt my determinations of declination and 

 those of Mr. Pond, Dr. Brinklcy, and others, have excited 

 attention in England, and will consequently occasion fresh 

 inquiries, which probably will remove the doubts which now 

 exist. 



' From M.ScIiuinaclier's Astronoiiiisr/ir Xmhrkliliit, Xn. .'!2. 



Your 



