UTILIZATION OF SOLAR ENERGY ACKERMANN. 149 



He then gives a table of four tests of one hour each, varying from 

 9 a. m. to 4 p. m., and goes on to say : 



From these experiments It has been deduced that the amount of heat given 

 off per square foot per minute is about equal to 1.3 (major) calories (equal to 

 1.4 mLiior calories per square-centimeter-minute). For our zone [probably 

 Laibach, Austria], then, the mean value of e may be set down as 1.3. 



The work of August Mouchot in connection with the utilization of 

 solar energy was certainly of great importance. It is recorded in his 

 book entitled " La Chaleur solaire et les Applications industrielles," 

 second edition, 1879; but, as with other workers in this field, he gives 

 extremely meager information as to results of • experiments. 



Mouchot started his solar work in 18(30 and took out his first patent, 

 No. 48,622, on March 4, 1861. In the first edition of his above-named 

 work (p. 231) he stated that theoreticall}^, on an average, 86 square 

 feet of reflecting surface are i'e(|uired for 1 horsepower. Then, to 

 allow for losses, he doubled the area, thus making it 172 square feet. 

 It is to be noted that he referred to reflecting surface and not the area 

 of radiation collected, which would almost certainly be a smaller 

 quantity. 



On page 195 he described one of his boilers as having a capacity of 

 3| pints. It consisted of two cylindrical concentric copper vessels 

 with domed tops and the water space between them. The vertical 

 height of the outer vessel was 16 inches. The boiler was covered by 

 a bell glass and plnced at the focus of a reflector. The water boiled 

 in one hour from an initial temperature of 50° F. 



In August, 1866, Emperor Napoleon III of France saw Mouchot's 

 first solar engine at work in Paris, and in 1872 ]\Iouchot (with the 

 monetary assistance of the French Government) constructed another 

 sun boiler. This was described by M. L. Simonin in tlie Revue Des 

 Deux Mondes of May 1, 1876, as follows: 



The traveler who visits the library of Tours sees in the courtyard In front a 

 strange-looking apparatus. Imagine an immense truncated cone, a mammoth 

 lamp shade, with its concavity directed skyward. This apparatus is of copper, 

 coated on the inside with very thin silver leaf. On the small base of the trun- 

 cated cone rests a copper cylinder, blackened on the outside, its vertical axis 

 being identical with that of the cone. This cylinder, suri-ounded as it were by a 

 great collar, terminates above in a hemispherical cap, so that it looks like an 

 enormous thimble, and is covered with a bell glass of the same shape. 



This curious apparatus is nothing else but a solar receiver — or, in other words, 

 a boiler — in which water is made to boil by the heat rays of the sun. This 

 steam generator is designed to raise water to the boiling point and beyond by 

 means of the solar rays, which are thrown upon the cylinder by the silvered 

 inner surface of the conical reflector. The boiler receives Avater up to two- 

 thirds of its capacity through a feed pipe. A glass tube and a steam gauge 

 comuumicatiug with the inside of the generator, and attached to the outside of 

 the reflector, indicate both the leA'el of the water and the pressure of the steam. 

 Finally, there is a safety valve to let off the steam when the pressure is greater 



