278 Dr. Herschel's Investigation of the Powers 



permit the eye to bear the sun. This destroyed all distinctness ; 

 and also permitted some heat to come to the eye, by transmit- 

 ting chiefly red rays. 



No. 3. I applied two white glasses, with pitch between them, 

 to the telescope ; and found that it made the sun appear of a 

 scarlet colour. They transmitted some heat; and distinctness 

 was greatly injured. 



No 4. I used a very dark green glass, to stop heat; and 

 behind it, or towards the eye, I placed a red glass, to stop light. 

 The first glimpse I had of the sun, was accompanied with a 

 sensation of heat ; distinctness also was materially injured. 



No. 5. I used a dark green and a pale red ; but, the sun not 

 being sufficiently darkened, I smoked the red glass, and, put- 

 ting a small partition between the two, placed the smoke 

 towards the green glass. This took off the exuberance of light; 

 but did not remedy the inconvenience arising from heat. 



No. 6\ I used two pale green glasses ; smoking that next to 

 the eye, and placing it as in No. 5, so that the smoke might be 

 inclosed between the two. This acted incomparably well ; but, 

 in a very short time, the heat which passed the first glass, 

 (though not the second, for I felt no sensation of it in the eye,) 

 disordered the smoke, by drawing it up into little blisters or 

 stars, which let through light ; and this composition, therefore, - 

 soon became useless. 



No. 7. I used two dark green glasses, one of them smoked, 

 as in No. 5. These also acted well ; but became useless, for the 

 reason assigned in No. 6, though somewhat less smoke had 

 been required than in the former composition. I felt no heat. 



No. 8. I used one pale green, with a dark green smoked 

 glass upon it, as in No. 5. It bore an aperture of 4 inches very 



