148 



ANNUAL OF SCIENTIFIC DISCOVERY. 



lias boon also communicated to Silliman's Journal, November, 1800, by 

 Y. H. Stoirr, Esq., of Boston. Instead of lamp shades, however, flat sheets 

 of jrlass (ordinary window-panes), six by eight inches, were fitted to a rack 

 of blackened wire, which was fastened to a photometer bar (one hundred 

 inrlK-s long), at a distance of three feet from the gas-light. The illuminat- 

 ing power of the gas used was equal to sixteen candles, consuming, by cal- 

 culation, one hundred and twenty grains of spermaceti per hour. The results 

 obtained were as follows : 



I 



" 



-.1 



TV 



i 



Description of glass. 



Thick English plate, 



Crystal plate, ... 



English crown, 



" Double English," window-glass, 



"Double German,"! 



" Single German," 1 



Double German, ground, 2 



Single German, ground, 2 



Berkshire (Mass.), grouud,2 . 



Berkshire enamelled, i. e., ground \ 

 only upon portions of its sur- /- T 5" 

 face, small figure, \ 



" Orange-colored " window-glass, 



"Purple" " " " 



"Ruby" " " " 



"Green" " " " 



A porcelain transparency (Tyrolese 

 Hunter), 



Thickness of glass. 



i of an inch, 



3 



tt 



1C 



Loss of light. 



6.15 per cent. 



8.61 " 

 13.08 " 



9.39 

 13.00 



4.27 

 62.34 

 65.75 

 62.74 



51.23 



1C 



97.68 



" The term ' loss of light/ " says Mr. Storer, " does not at first seem to be 

 strictly appropriate, for a very considerable portion of the light not trans- 

 mitted by a glass shade might be reflected against the walls of the apart- 

 ment in which the lamp is burning, and thus aid in the general illumination 

 of the room. The meaning of the expression is, however, perfectly evident; 

 and there can be no doubt that the numbers given express as accurately as 

 the circumstances of the case admit the actual diminution in the amount of 

 light falling, for example, upon the pages of a book held near its source, 

 which would be occasioned by the interposition of the shades enumerated in 

 the tables." 



In commenting upon this subject, the editor of Silliman's Journal further 

 remarks : 



1 Among the Boston dealers, the term German is applied to glasses of Belgian 

 manufacture. 



t The enormous resistance to the passage of light which is offered by ground glass 

 is certainly worthy the attention of those using it for windows, etc. 



The discrepancy between Mr. King's results and my own, as regards ground 

 glass, may perhaps be owing to the fact that the window glass used by myself was 

 more coarsely ground than the lamp shades employed by him. 



