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 VIL, 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 ; ¢¢’ are the ends next the eyes, 
and cc, ¢'¢ 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 77". 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 ss 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. 
