188 ANNUAL OF SCIENTIFIC DISCOVERY. 



rodes the zinc which is not covered by the ink, and thus the design is brought 

 out ; from the plate thus engraved in relief, a gutta percha mold is taken, in 

 which copper is deposited to obtain the engraved plate, from which proofs 

 may be taken by the ordinary typographic press. 



OBSERVATIONS OX THE MEANS OF INCREASING THE QUANTITY 

 OF HEAT DERIVED FROM COMBUSTION. 



The following is an abstract of a paper presented to the American Associa- 

 tion, by Professor Henry, at the Providence meeting : Rumford noticed the 

 fact that a mixture of clay with sea coal caused more heat to be evolved than 

 he was able to produce with coal alone. He found that when the sides and 

 back of a chimney are lined with fire-brick, they give out more heat than the 

 coal itself. Eumford also suggested that the bottom of the fire grate be 

 covered with balls of clay, in order that a greater radiation of heat may take 

 place. He gives, however, no account of experiments definitely made, or of 

 the cause of the phenomena he witnessed. In reading the account of his ex- 

 periments, his results appear at first sight paradoxical : but Rumford was an 

 eminent experimenter, and the facts he has stated in connection with various 

 branches of physical science are found to be supported as science advances. 



After expounding Rumford's plan, Professor Henry said the idea had oc- 

 curred to him to repeat the count's experiments, or to make further researches 

 with the aid of such appliances as modem science furnishes. These investi- 

 gations had been prosecuted for a number of years. His method of operating 

 was as follows : He took a thermo-electric apparatus, applied a tube at the 

 end of the instrument so as to circumscribe the field of radiation, and placed 

 it near a coal fire. The idea was to see if fire could be made hotter. And it 

 was. The result confirmed the assertions of Rumford. A coal fire, however, 

 was difficult to manage ; the coal was anthracite, and not bituminous : the 

 latter was probably employed by Rurnford. The experiment was repeated 

 with ordinary flame with the flame of hydrogen and that produced by the 

 combustion of alcohol, placed at such a distance that the needle of a galvanom- 

 eter stood at 15. A platinum wire, coiled, was inserted hi the flame, when 

 the radiation increased, and the galvanometer marked 27. Subsequent ex- 

 periments were made with carbonate of lime, sulphate of lime, stone coal, fire 

 clay, etc. These substances were introduced into flame and the degree of 

 radiation marked. Different substances produced different effects; the greatest 

 effect being produced by carbonate of lime. Precise results were not ascer- 

 tained. "We could not suppose that the absolute amount of heat was increased. 

 The most probable conjecture Professor Henry thought was, that the heat of 

 combination was converted into radiant heat. To test this he had placed a 

 platinum wire in the apex of a flame and introduced a slip of mica, one-fifth 

 of an inch in breadth, vertically beneath it. The wire immediately diminished 

 in intensity of light and of radiant heat, so that while the mica itself was 

 radiant with light and heat, it was evident that its introduction cooled the 

 flame above it, verifying the idea that the intensity of radiation was produced 

 at the expense of the heat of combination. So if fuel was to be employed in 



