WILLIAM SIEMENS, F.R.S. 63 



but which we should nevertheless keep steadfastly before our eyes* 

 Thus a pound of ordinary coal is capable of producing 12,000 Fahr. 

 units of heat, which equal 9,240,000 foot Ibs. or units of force, 

 whereas the very best performances of our pumping engines do 

 not exceed the limit of 1,000,000 foot Ibs. of force per pound of 

 cnal condensed. In like manner one pound of coal should be 

 capable of heating 83 pounds of iron to the welding point (of 

 say 3000 Fahr.), whereas, in an ordinary furnace, not two 

 pounds of iron are so heated with one pound of coal. These 

 figures serve to show the great field for further improvement that 

 lies yet before us. 



Although heat may be said to be the moving principle by which 

 all things in nature are accomplished, an excess of it is not only 

 hurtful to some of our processes, such as brewing, and destructive 

 to otfr nutriments, but to those living in hot climates, or sitting 

 in crowded rooms, an excess of temperature is fully as great a 

 source of discomfort as excessive cold can be. Why then, may I 

 ask, should we not resort to refrigeration in summer as well 

 as to calorification in winter, if it can be shown that the one can 

 be done at nearly the same cost as the other ? So long as we rely 

 for refrigeration upon our ice-cellers, or upon importation of ice 

 from distant parts, we shall have to look upon it as a costly luxury 

 only ; but by the use of properly constructed machines, it will be 

 possible, I believe, to produce refrigeration at an extremely 

 moderate expenditure of fuel and labour. A machine has already 

 been constructed capable of producing 9 Ibs. of ice (or its 

 equivalent) for 1 Ib. of coal, whereas the equivalent values of 

 positive heat developed in the combustion of 1 Ib. of coal and of 

 negative heat residing in 1 Ib. of ice is about as 12,000 to 170, or as 

 1 to 70. This result already justifies the employment of re- 

 frigerating machines upon a large scale ; but it is hard to say what 

 practical results may yet be reached with an improved machine 

 on strictly dynamical principles, because such a machine seems not 

 to be tied in its results to any definite theoretical limits. In 

 changing, for example, a pound of water from the liquid into the 

 gaseous state, a given number of units of heat are required, that 

 may be produced by combustion of coal or by the expenditure of 

 force, but in changing the same pound of water into ice, 

 heat is not lost but gained in the operation, which heat must 



