The tercentenary of the compound microscope : an inaugural address delivered November 7, 1890 to the Scottish Microscopical Society / by W. Rutherford.

  • William Rutherford
Date:
1891
Catalogue details

Licence: Public Domain Mark

Credit: The tercentenary of the compound microscope : an inaugural address delivered November 7, 1890 to the Scottish Microscopical Society / by W. Rutherford. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

    17/26 (page 15)
    T 1 Tiin rliftpvpnre arises from tne wavcb oi ucni^ tun.,o.gc. th„„ those of “'TliSnlatioos of light, like those on the sniface of a liquid, are ^rs,S rn^uTdr r S;t\;rerir -It the s-ime moment. Therefore, when the opposite phases of the ^dulatSrrureuteut are e,taetlj- couuter-balaneed, there ,s rest hy ru“f»ir./««e, .'hift the eoineidence of srmdar the resulting wave. One may observe these effects in watei waves, hut they are still more evident on the surface of mercury. If m an oval trough half filled with mercury one suddenly dimple sui- face at one of the foci, the waves spread to the sides, and aie reflected to and fro, producing a beautiful system of mterfeience lines. Luminor/s undulations give rise to similar though much 1^ evident results, because of the extreme shortness of t^e waves, and the invisibility of the medium in which they are J interference of light may be shown by several methods. Ihe most intellio-ible is one of those devised by Fresnel, in which a system of waves“of red or green light slightly diverging from a common source is received on two closely adjacent straight-edged plain minors o steel or of plate-glass blackened behind, and inclined tow aids eac other at an Lgle of 180° or less (fig. 2, m, n). The waves falling on the inclined surfaces are reflected in two systems that intersect^each other at an angle suitable for the production of interference pheno- mena. When the light falls on a screen of ground glass there is a brio-ht central band, with a fringe of alternate dark and ligdit bands on each side, the dark bands arising from the coincidence of opposite phases, the light bands from the coiircidence of similar phases of the two sets of waves. . . , n The phenomena produced by Fresnel s mirrors arise simply from the interference of luminous waves ; those produced by a slit arise from the difradioii as well as the iiif.erference of the wave motion. Diffraction is not ]ieculiar to light. All undulatory moveincnts may be diffracted. The prinnjxti wave that spreads from a imint of disturbance on the surface of a liquid is the resultant of an infinite number of elcvienlari/ wotionx of the molecules. Every molecule implicated in the spreading wave successively becomes a centre from which an elementary wave system radiates. But in the mutual • These pheaoinciia may he mnre simi'ly, though le.ss dearly, shown hy the ordinary method ot |.hidng a slit in a iiiceu of blank card hoard or paper holoro a lamp, and looking at it tlirongh a line drawn wilh a needle acro.s.s a slip ol .smoked glass. The blue dillVnelion hands cannot be seen, however, nidess the lamp is eonipletely shaded to cut (dfall dilluse light.