364 m. PONTON, ESQ., ON SOLAR LIGHT 



of their diameters were two-and-a-half inches apart, but with the means of 

 slightly varying this distance, so as to bring the apertures exactly opposite the 

 pupils of the two eyes. At the end of the tubes next the eye was an aperture of 

 about a quarter of an inch in diameter, in which was inserted a piece of blue 

 glass. Outside of these were placed slides, into which the perforated slips of lead 

 might be introduced, in such a manner as to prevent their apertures from touch- 

 ing the surface of the paper, for fear of the entrance of minute fibres. At the 

 ends of the tubes farthest from the eyes were simple apertures of about a quarter 

 of an inch in diameter. To each of these farthest ends was attached, at the inner 

 edge, a piece of card, which, after projecting outwards, about an inch and a half, 

 was bent round at a right angle, so as to face the end of the tube. These pieces 

 of card were covered on the outside with black paper, and on the inside with 

 the prepared blue paper before described. The lower part of the card was at- 

 tached to the lower end of the tube by a similar piece of card, also lined with the 

 blue paper ; and there was thus formed, at the further end of each tube, a small 

 rectangular box, open at the top and the outer side, and lined throughout with 

 the blue paper. To each of these boxes were closely fitted covers, which could 

 be put on and removed at pleasure. The cross piece connecting the two tubes 

 was fastened to a telescope stand, so as to[place the tubes horizontally at the level 

 of the eyes. When so adjusted, the surfaces destined to receive the light were 

 vertical. 



In Plaie VIII., fig. 1, is shown a bird's-eye view of the two tubes PQ and RS ; 

 while XY is the cross piece by which they are attached, and on which they 

 slide horizontally, so as to adjust their distance ; ee are the ends next the eyes, 

 and c c, c c are the cards fastened to the farther ends, on which the light is to 

 fall. Fig. 2 is a central cross-section, showing how the tubes are connected by 

 the cross piece, and the latter with the telescope stand T. Fig. 3 shows the two 

 ends next the eyes, with the perforated slips of lead inserted in the slides. 

 Fig. 4 shows the farther end of the tube, prepared to receive the sun-light, with 

 the direction of the rays r r. Fig. 5 shows the farther end of the other tube, fur- 

 nished with a small screen s to exclude the direct rays of the sun, and leave the 

 receiving surface illuminated by the mere light of the sky. Fig. 6 shows the 

 end of the sun-tube, disposed for the lamp ; the ring / being the argand burner, 

 surrounded by a screen s s to confine the light. This screen was covered with 

 black paper outside, and lined with white paper inside, so as to give the lamp- 

 light the benefit of its reflection. There was another screen, not shown in the 

 figure, placed over the argand, with a hole only sufficient to admit the glass chim- 

 ney. By this arrangement, all light was excluded from the little box, except 

 that of the lamp, whose flame was placed in such a position that the rays fell on 

 the receiving surface at a horizontal angle of about 45 degrees, the surface of 

 the flame being about two inches from the receiving surface. 



