L. MECHANICS AND ENGINEERING. 481 



of Dillons' which assumes the calorific effect of coal free from 

 moisture to be the sum of the calorific effects of all its com- 

 bustible elements, less the proportion of hydrogen required 

 to form water with the whole of its oxygen. The coals in 

 question gave experimentally a calorific effect from three 

 to twelve per cent, higher than that obtained by the cal- 

 culation according to Dulong's law. Among the numer- 

 ical values quoted by Isherwood, the following are of in- 

 terest : 



"The number of pounds of water that were raised 1 Fahr. 

 in temperature by the burning of one pound of crude coal or 

 lignite, as found by direct experiment, was for 



The Groucheaski anthracite 14. 139 



The Mioucki coal 15.383 



The Galouboski coal 13.509 



The Tonla lignite 10.429 



These numbers are in all cases, as above stated, considerably 

 less than those calculated according; to Dulono-'s law. 



"The Welsh coals ordinarily used in the British Navy are 

 the Bwelf and the Powell, which respectively have calorific ef- 

 fects of 15.804 and 16.108 of the above units." 1 Z>, IX., 

 370. 



FILLING THE DEPRESSION IN THE DESERT OF SAHARA. 



Considerable discussion is now going on in reference to 

 the propriety of the proposed plan of the French government 

 of filling a depression in the Sahara Desert by allowing the 

 entrance of water from the Mediterranean ; many questions 

 arising as to the effect, not only upon the country, but upon 

 the regions north of the Mediterranean. 



It is well known that the sirocco (or the Fohn of the Ger- 

 mans), after crossing the Mediterranean, expends itself upon 

 the snows and glaciers of the Alps, and tends in a considera- 

 ble degree to prevent their undue extension, as in an earlier 

 geological period. Many persons fear that, should this de- 

 pression be filled with water, the proper amount of dry heat 

 will not be produced to regulate the glaciers, and that in 

 consequence they will probably extend far into the plains, 

 and perhaps in a measure reproduce the climatic conditions 

 that existed during the reindeer period, the evidences of 

 which are so abundant in Southern Europe. 



X 



