MECHANICS AND USEFUL ARTS. 97 



Showing an increase of 40 per cent, over the old rule of correc- 

 tion. 



From experiments with different burners and with gas from 

 rich coals, Prof. Silliman says : — 



"A comparison of the results will show that the coincidences 

 with the requirements of the theorem of Farmer are, within the 

 limits assigned, too numerous, and too closely accordant, to be 

 considered as otherwise than pointing clearly to its general truth. 

 A rigorous demonstration cannot be expected, as there are too 

 many variable functions of unknown value involved in the best 

 methods at present known for photometric measurements, to per- 

 mit more -than an aj^proximate proof of its general accuracy. 

 Ever}'^ photometric observer must recognize its importance, and 

 the necessity in his observations of bringing the consumptions of 

 gas and sperm to the agreed standard. 



*' To the consumer of gas the evident inference from the data 

 here presented is that where it is important to obtain a maximum 

 of economical effect from the consumption of a given volume of 

 illuminating gas, this result is best obtained by the use of bux'u- 

 ers of ample flow. 



*' Where a moderate light of equal diffusion is required over a 

 large space, as in public rooms, it may be expedient to use nu- 

 merous small jets ; but when the maximum intensity obtainable 

 from a given volume of illuminating gas is desired, intensity of 

 burners of large consumption is plainly indicated." — Abstract 

 from a paper read hy Prof. Silliman at the Salem meeting of the 

 Am. Association, Aug., 1869. 



GAS FROM WOOD. 



The following fact may be mentioned in connection with the 

 manufacture of gas from wood. In those countries where this 

 material is abundant, and coal not accessible, wood, aided by the 

 addition of some substance furnishing a rich hydro-carbon, may 

 be made to furnish a very useful illuminating gas, and an eco- 

 nomical one, especially when the residue in the retorts and mate- 

 rial distilled with the gas can be rendered serviceable. In Co- 

 burg, Canada, it is said to have been used advantageously, fur- 

 nishing a good gas and a valuable residue, namely : — 



Two parts pine wood. 



One part hard wood. 



One part bones. 



The residue in the retorts is an excellent charcoal for bleaching 

 purposes, and the other residues are quite serviceable. Where 

 bones cannot be obtained, offal and other coarse animal matter 

 can be used to mix with the wood. This suggestion is worthy 

 of consideration, especially for many small towns peculiarly sit- 

 uated. 



