The Transactions of the Microscopical Society of London, Band 2

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John Van Voorst, 1854
 

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Seite 204 - ... and which consequently are the extreme available rays. A very perfect instrument for measuring the angle of aperture, designed by Mr. Gillett, was then explained : this consists of two microscopes, the optical axes of which may be adjusted to coincidence. One of these is attached horizontally to the traversing arm of a horizontal graduated circle, and is adjusted so that the point of a needle, made to coincide with the axis of motion of the movable arm, may be in focus and in the centre of the...
Seite 204 - The other microscope, to which the object-glass to be examined is attached, is fixed, and so adjusted that the point of the same needle may be in focus in the centre of its field. The eye-piece of the latter is then removed, and a cap with a very small aperture is substituted, close to which a lamp is placed. It is evident that the rays transmitted by the aperture will pursue the...
Seite 136 - ... of the fine motion, and move it briskly backwards and forwards in both directions from the first position. Observe the expansion of the dark outline of the object, both when within and when without the focus. If the greater expansion, or coma, is when the object is without the focus, or...
Seite 293 - May 24, 1853." On the probable Errors of the Eye and the Ear in Transit Observations. By the Rev. TR Robinson, DD, President of the Royal Irish Academy. With respect to the usual mode of recording transit observations, and the invention recently introduced at American observatories for accomplishing the same object by means of electricity, the author remarks, that the two systems not merely employ different senses to co-operate with sight, but that...
Seite 76 - The area of the delta being about 13,600 square statute miles, and the quantity of solid matter annually brought down by the river 3,702,758,400 cubic feet, it must have taken 67,000 years for the formation of the whole...
Seite 212 - This assertion seems to me to be extraordinary, and very like saying that an aperture of 85° or 90° will do everything that is required. I have invariably found that when very difficult tests are mounted in balsam I cannot discover the markings, and certainly the reasons herein given will account for it. It is to be hoped that the American opticians have discovered some new and peculiar principle in object-glasses, that will render a smaller amount of aperture serviceable ; but however this may...
Seite 192 - I now suspect to be an ergot upon which the animal had fed. The plant consisted of oblong or oval vesicular bodies, apparently thickened at the poles, and filled with a colourless liquid ; but this appearance more probably arose from the cells being distended with a single large, transparent, colourless, amorphous globule, which pressed a small existing amount of protoplasma to each end of the cavity. The cells were single, or in rows, to eighteen in number. Frequently a single cell of comparatively...
Seite 18 - The light through the objective, which impinges upon a, is that part of it which enters the prism refracted to the left, so that it meets with the reflecting surface b. Suffering total reflection, it emerges from the surface c, where, from the necessary identity of the immergent and emergent angles, it is refracted to the left, so as exactly to compensate for its previous refraction to the left.
Seite 91 - ... it acquires no gastric teeth, and never attains perfection in form or size. If, at the same time, it be confined within a narrow cell, or space, it grows only to such a size as will enable it to move about freely; thus adapting itself to the necessities of its restricted state of existence.
Seite 292 - ... The refraction of the light out of the field of the microscope or beyond the angle of aperture of the object-glass is the ordinary cause of the outlines of objects becoming visible ; and in these cases, an increase of the angular aperture of the object-glass will impair their distinctness, because it will allow of the admission of those rays which would otherwise have been refracted from the field, and the margins will become more luminous and less contrasted with the luminous field. The cause...

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