A text-book of physics, largely experimentalOn the Harvard college "Descriptive list of elementary physical experiments." . compared, and L the other; R therod, AB the screen, and SL and SL* the shadows. The lamps shouldbe so arranged that lines drawn from their centres to the centre of Rwill make nearly equal angles at R with the line CD, drawn at rightangles to the screen through the centre of R, and on this line CDthe observer should be placed. The shadows should be near eachother, but must not overlap. It is plain that the shadow corresponding to L is illuminated bylight from Lf, and that
A text-book of physics, largely experimentalOn the Harvard college "Descriptive list of elementary physical experiments." . compared, and L the other; R therod, AB the screen, and SL and SL* the shadows. The lamps shouldbe so arranged that lines drawn from their centres to the centre of Rwill make nearly equal angles at R with the line CD, drawn at rightangles to the screen through the centre of R, and on this line CDthe observer should be placed. The shadows should be near eachother, but must not overlap. It is plain that the shadow corresponding to L is illuminated bylight from Lf, and that the one corresponding to L is illuminatedby light from L. Place the lamps equidistant from the rod, and, shielding the eyesfrom the direct light of the flames, adjust the flames, turned edge-wise to the rod, until the shadows are of equal darkness. Then turn one of the lamps about in place until its flame is flat-wise to the rod, and compare the shadows again, fixing the attentionupon the middle of the more blurred one. If the shadows still appearto be of equal darkness, record the fact. If they do not, move one of A. FIG. 91. the lamps toward or from the rod until the shadows appear equallydark, and then record the distance of each flame from the corre-sponding shadow. Try each lamp in turn flatwise, the other being edgewise. Be-tween the trials test the flames again in their original position, tomake sure that they are still equal. If, on the whole, it appears that one aspect of the flame, broad-side or edge, is more effective than the other, estimate the relativelight-giving power of the two aspects from the measured distances,making use of the law of inverse square. NATURE OF LIGHT; VISIBILITY OF OBJECTS. 147 124. Effect on Light of the Body on which it Falls. — When light-rays meet the surface of a body they may be: a. Regularly reflected : that is, sent off from the surfacein a direction which can be calculated or foretold, if weknow the direction in which they are to s
Size: 2691px × 928px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, bookpublishe, booksubjectphysics
