478 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



The loss of light by the use of shades of any kind, and par- 

 ticularly those of ground glass, is very considerable. Mr. Wil- 

 liam King of Liverpool presents the following results in the 

 London Journal of Gas Lighting : Loss of light 



Description of shade. percent. 



Clear glass 10.57 



Ground glass (entire surface ground) 29.48 



Smooth opal 52.83 



Ground opal 55.85 



Ground opal, ornamented with painted figures, the figures 



intervening between the burner and photometer screen,. *73.98 



Recent experiments by Mr. Frank H. Storer, for the Boston 



Gas Light Company, show even a greater loss of light. He 



obtains the following results : Loss of light, 



Description of glass. Thickness of glass. percent. 



Thick English plate | of an inch. 6.15 



Crystal plate ^ " 8.61 



English crown _ | " 13.08 



Double English window glass | " 9.39 



Double German window glass ^ " 13.00 



Single German window glass 1.16 " 4.27 



Double German, ground | " 62.34 



Single German, ground 1.16 " 65.75 



Berkshire (Mass.), ground 1.16 " 62.74 



Berkshire, enameled, i. e., ground only 



upon portions of its surface — small 



figure 1.16 " 51.23 



*Orange-colored window glass 1.16 " 34.48 



*Purple-colored " ^ " 85.11 



*Ruby-colored " 1.16 " 89.62 



*Green-colored " 1.16 " 81.95 



A porcelain transparency, (Tyrolese 



Hunter) 1.16 " 97.68 



The greater portion of this light which is lost is converted . 

 into heat. 



THE CUT-OFF IN THE STEAM ENGINE. 



Mr. W. A. Bartlett moved that the subject for discussion the 

 next evening should be the " Theoretical and practical value of 

 the cut-off in the steam engine." 



Adjourned to Thursday evening next, June 21, at 8 o'clock. 



• As used for church windows, &o. 



