This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1907 Excerpt: ...would be that of the violet ray. Thus, in order that v' v may be the violet ray, the deviation produced by the lens at R, R' in the red ray must be greater than that produced at v, v in the violet ray. If the angle between the faces of the lens at R, R' were equal or less than that at v, v' this would clearly be ...
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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1907 Excerpt: ...would be that of the violet ray. Thus, in order that v' v may be the violet ray, the deviation produced by the lens at R, R' in the red ray must be greater than that produced at v, v in the violet ray. If the angle between the faces of the lens at R, R' were equal or less than that at v, v' this would clearly be impossible, but since the angle at R, R' is greater than that at v, v', it is possible for the deviation of the red light at R to be greater than that of the violet light at v; that is to say, it is possible for the violet ray to emerge in the direction v' v parallel to the red ray R-r. We can then combine two convex lenses to form an achromatic eye-piece. The dispersion produced by the first lens is compensated in the second from the fact that the red light falls further from the centre than the violet, at a point, therefore, where the refracting angle of the prism which would produce the same deviation as the lens is greater than at the point of incidence of the violet light. A similar argument will apply to the case in which the light cuts the axis of the lenses between the two. In this case (fig. 107) v will be further away from the centre of the second lens than R, and in order that the two colours may emerge parallel, the violet light must be more deviated than the red. This it will be for two reasons. Firstly, because it is violet light and is therefore more deviated than red incident in the direction T v would be; and secondly, because the faces of the lens at v, v' are inclined to each other at a greater angle than they are at R, R', So that red light travelling along T V would be more deviated than red light along s R; thus a fortiori the violet ray T v is more deviated by the second lens than the Fig. 107. red ray Sr, and the two may emer...
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