Page:Popular Science Monthly Volume 5.djvu/743

Rh the materials ordinarily employed for purposes of illumination. Actual experiment, however, in the use of these machines in French lighthouses, has shown that these figures require important modifications" ("United States Commissioner's Report to the Paris Exposition, 1867," vol. iii., p. 421).

The French Commission, in view of the experience gained by the establishment of the light at La Hève, did not advocate the extension of the use of the electric light to light-house illumination in general. The expense of maintaining the electric light at Dungeness, irrespective of the original cost, was estimated to be £758 18s. 9d. per annum. M. Becquerel evidently did not take into account in his calculation the original cost of the machine; and the expense of the light at Dungeness would be modified by the greater cheapness of the more improved forms of engines.

For several years it has been rumored that various steamships were to be furnished with the electric light instead of the old well-established masthead-light. No trial has yet been made. The cost of the apparatus, together with the imperfect means hitherto devised for maintaining the light constant, has deterred, apparently, the owners of steamship lines from making a change in this direction. When we reflect that the best masthead-light now in use can be seen only from four to five miles—by some authorities stated from three to four—and in a fog at night is practically not visible more than the length of a steamship ahead, it is not surprising that the general public look earnestly for a change for the better. The experience which the use of the electric light in light-houses has given us is, on the whole, favorable to an extension of the use of the light to steamships. There is no question of the superiority of the electric light over other powerful lights available for steamships, when the great intensity of the light and the compactness of the necessary apparatus are considered. The following is an estimate of the probable cost of fitting steamships with an electric light, together with its maintenance:

Suppose that the vessel made 18 trips during the year, of 12 days each (216 days), suppose that the electric light was used 10 hours each night (2,160 hours), giving about 53 cents as the cost per hour,