MECHANICS AND USEFUL ARTS. 45 



pies of the Mechanical Action of Heat, founded on the idea that heat is not 

 u substance, but a form of energy, are making their way amongst practical 

 men, and are being usefully applied by them. As a means of facilitating 

 that progress, by putting the expression of those principles into a shape 

 more familiar to practical engineers than their present form, it was recently 

 suggested by Mr. Stephenson, that, instead of the Unit of Heat commonly 

 employed in scientific treatises, viz., so much heat as one pound of water 

 requires in order to raise its temperature by one degree, quantities of heat 

 should be expressed in terms of a unit which practical men oftener have 

 occasion to think of viz., so much heat as one pound of water at 212 of 

 Fahrenheit requires, in order to convert it into steam, at the same tempera- 

 ture; or what is commonly called 'the latent heat of one pound of steam 

 at 212 of Fahrenheit;' being, in fact, the unit of heat now commonly em- 

 ployed in comparing the effects of different kinds of fuel and different forms 

 of furnace. This suggestion of Mr. Stephenson appears to be well worthy 

 of consideration and discussion. The following is a comparison of different 

 units of quantity of heat, British and French, reduced to their equivalents in 

 units of mechanical energy, as a common standard of comparison, based on 

 the experiments of Joule : 



BRITISH UNITS. Equivalent energy in 



foot-pounds. 



One degree of Fahrenheit's scale in a pound of water, . . . 772 

 One degree of the Centigrade scale in a pound of water, . . 1399 

 Latent heat of one pound of atmospheric steam, .... 745750 



FRENCH UNITS. Equivalent energy in 



kilogrammetres. 



One degree of the Centigrade scale in a kilogramme of water, . 4237 

 Latent heat of one kilogramme of atmospheric steam, . . . 22730 

 One kilogrammetre = 7-23314 foot-pounds. 

 One loot-pound = 138253 kilogrammetres." 



TRY-COCK FOR STEAM-BOILERS. 



This invention combines in one steam-boiler try-cock, all the advantages 

 secured from three or more try-cocks of the present construction. Its nov- 

 elty lies in the use of a straight hollow tube, inserted in the end of the 

 boiler, and arranged to move up and down on a hollow axis ; said axis com- 

 municating with the passage of the tube, and with the passage of a try- 

 cock. The tube has a pointer on its outer end, and opposite the same a dial 

 or under plate is placed. A spring holds the under end of the tube down, 

 and thus keeps the inner end above the level of the water in the boiler. By 

 this arrangement, by simply elevating the outer end of the tube and open- 

 ing the cock, the same end will be brought down into the water, and the 

 height of the water indicated ; for as soon as the tube enters the water, the 

 latter will be squirted through the tube, and escape at the try-cock. As soon 

 as this occurs, the engineer casts his eye to the dial, and ascertains the 

 height of the water in the boiler. The inventor of this device is James 

 Cummings, of Boston, Mass. Scientific American. 



COALS AND FURNACES BURNING SMOKE. 



It has long been a most desirable object, in burning bituminous coals, to 

 consume all the smoke; and in England a law has been passed for the pur-' 



