ASTRONOMICAL PHENOMENA AND PROGRESS. 



43 



answer as well on a large as It doe* on a small scale ! 

 : .llowing reply will effectually dispose of this 

 pregnant query. It is not necessary, nor intended, to 

 enlarge in future the size of the apparatus by means 

 of which the solar intensity haa been successfully 

 concentrated, and the temperature sufficiently ele- 

 vated to venerate steam for the engine* which have 

 been built. The maximum size aaopted has been 

 adequate to utilize the radiant heat of a sunbeam of 

 live square feet section. The employment of 

 an increased number of such structures will therefore 

 be resorted to when greater power in wanted, as we 

 increase the number ot hands when we desire to per- 

 form an additional amount of work. The motor itself, 

 the eteara cylinder and other parts, will obviously 

 be proportioned as at present with reference to the 

 pressure of steam employed and the work to be done. 



Agreeably to our introductory remarks, it is not 

 proposed, in the first instance, to apply solar engines 

 in places where there is not steady sunshine. The 

 isolated districts of the earth's surface suffering from 

 an excess of solar heat being very numerous, our 

 space only admits of a glance at the sunburnt conti- 

 nents. An examination of the extent of these will 

 show that the field for the solar engine, even with 

 the proposed restriction, is not very contracted. 

 There is a rainless region extending from the north- 

 west coast of Africa to Mongolia, 9,000 miles in 

 length, and nearly 1,000 miles wide. Besides the 

 Northern African "desert*, this region includes the 

 southern coast of the Mediterranean east of the 

 Gulf of Cabes, Upper Egypt, the eastern and part 

 of the western coast of the IZed Sea, part of Syria, 

 the eastern part of the countries watered by the Eu- 

 phrates and Tigris, Eastern Arabia, the greater part 

 of Persia, the extreme western part of China, Thibet, 

 and lastly, Mongolia, In the western hemisphere. 

 Lower California, the table-land of Mexico and 

 Guatemala, and the west coast of South America, 

 for a distance of more than 2,000 miles, suffer from 

 continuous intense radiant heat. 



Computations of the solar energy wasted on the 

 vast areas thus specified would present an amount of 

 dynamic force almost beyond conception. Let us, 

 therefore, merely estimate the mechanical force that 

 would result from utilizing the solar heat on a strip 

 of land, a single mile in width, along the rainless 

 -!i coast of America ; the southern coast of the 

 Mediterranean before referred to ; both sides of the 

 alluvial plain of the Nile in Upper Egypt ; both sides 

 of the Euphrates and Tigris for a 'distance of 400 

 miles above the Persian Gulf: and, finally, a strip 

 one mile wide along the rainless portions of the 

 shores of the Red Sea, before pointed out. The ag- 

 gregate length of these strips of land, selected on ac- 

 count of being accessible by water communication, 

 far exceeds 8,000 miles. Adopting this length and a 

 width of one mile as a basis for computation, it will 

 be seen that the assumed narrow belt of the sun- 

 burnt continents covers 223,000 millions of square 

 feet. Dividing this by the area necessary to produce 

 1-horse power, we learn that 22,809,000 solar engines, 

 each of 100-horse power, could be kept in constant 

 operation, nine hours a day, by utilizing only that 

 heat which is now wasted on a very small fraction of 

 the land extending along some of the water-fronts 

 of the sunburnt regions of the earth. 



It will be said that these extravagant figures are 

 devoid of practical significance. Due consideration, 

 however," cannot fail to convince us that the gradual 

 exhaustion of the coal-fields will inevitably cause 

 great changes in regard to international relations, in 

 favor of those countries which are in possession of 

 continuous sun-power. Upper Egypt, for instance, 

 will, in the course of time, derive signal advantage, 

 and attain a high political position, on account of her 

 perpetual sunshine and the consequent command of 

 unlimited motive force. The time will come when 

 Europe must stop her mills for the want of coal. 

 Upper Egypt, then, with her never ceasing sun- 



power, will invite the European manufacturer to re- 

 move his machinery and erect hU mill* on the firm 

 1 along the side* of the alluvial plum of the 

 Nil<-, where sufficient power can be obtained to en- 

 ut.l, him to run more spindles than a hundred Man- 

 chester*. 



(See alao 8w, K- I.IPSE OF.) 



Heat from the Moon. At the June meeting 

 of the Rojal Society the Earl of Ros.se gave an 

 account of more satisfactory experiments than 

 those previously reported, to determine the 

 amount of heat radiated from the moon. The 

 three-foot reflector at Parsonstown was em- 

 ployed as on former occasions. Earl Rosse first 

 ascertained the percentage of the moon's heat 

 which passes through glass, and found the 

 mean of nine observations, taken at various al- 

 titudes of the moon and distances from oppo- 

 sition, to be 11.88. Through the same glass, 

 86.8 percentage of the heat-rays of the sun 

 were transmitted. It seems, therefore, to be 

 clearly proved that there is no remarkable dif- 

 ference between the sun's and moon's heat in 

 regard to their power of passing through glass. 

 The experiment made during the previous sea- 

 son, to determine the ratio between the heat- 

 ing power of the moon and of the sun, was 

 repeated with more care, and the value found, 

 taking what appeared to be the most probable 

 mean heating power of full moon, as deter- 

 mined on various nights, was: moon's total 

 heat, 1 ; sun's total heat, 82,600. 



The observations were examined with a 

 view to ascertain how far the heating power 

 of the moon's rays varies with her altitude. 

 Owing to the interference of clouds, and the 

 limited range of altitude within which the ob- 

 servations were made, the results were not 

 given in detail, but Earl Rosse says that the 

 heating power of the lunar rays appears to 

 diminish with her altitude only about a third 

 as fast as the intensity of the solar chemical 

 rays, as ascertained by Roscoe and Thorpe. 

 An attempt was made to ascertain, by com- 

 paring two measurements of the moon's light 

 at different altitudes with two corresponding 

 measurements of her heat, whether our atmos- 

 phere intercepts the heat-rays to a greater 

 extent than the luminous rays. It was found 

 that, while the light was diminished with the 

 altitude in the proportion of about 3 to 1, the 

 diminution of the heat was in the proportion 

 of about 5 to 1. In consequence, however, of 

 much of the moon's light and heat being inter- 

 cepted by hazy clouds or condensed vapor, at 

 the lower altitude, the experiment was incon- 

 clusive as to the effect of a transparent atmos- 

 phere on the dark rays of heat. The observa- 

 tions showed a general accordance between tho 

 variation of the moon's radiant heat with her 

 phase, and the corresponding amount of her 

 light, as deduced by calculation. 



The Council of the Royal Society, at the 

 Annual Meeting in February, after stating tho 

 results of Lord Rosse's earlier observations on 

 Lunar Radiation (see AXXTAL CTCLOPJIDIA for 



