The President's Address
Journal of the Quekett Microscopical Club (1878)
Scientific Memoirs IV
[316] THE President said that the subject which he wished to bring before them that evening was a sort of contrivance which he had recently adopted himself, for the purpose of making dissections. They would all be aware that in a microscope to be used for delicate dissections, certain qualifications were absolutely essential. In the first place they must have perfect steadiness, the stand must be firmly and well supported, and be of sufficient strength and weight to bear the pressure put upon it without moving. Next it must be of convenient height, so that in working the hands might get a steady support; it should fulfil these two conditions, and yet not be so large as to be clumsy. The next point was as to the lenses; they should be of such a form as to give a maximum of power, and yet at the same time afford sufficient distance between them and the object to admit of needles being moved freely to an angle of 60° with the surface of the plate, because the efficiency of the needles obviously depended upon the angle at which they could be used, and if a lens were made with a wide face it would very often interfere with the movements of the needles. Then there was another point of still greater importance–when a careful dissection had been made, it often became desirable to examine it with a much higher power than the one which had served the purpose of preparation, and provision ought to be made to enable as high a power as was desired to be brought to bear without disturbing the object, and this could only be done by placing a compound body above the simple lens. The President [317] then exhibited the instrument which he had devised to meet these requirements, and pointed out that it consisted of a glass stage having a large aperture in the centre, and mounted horizontally upon three supports, one of which was formed by the pillar of the body; in this way it stood with great steadiness, and was strong enough to bear considerable pressure. The lens was carried by an arm projecting from the pillar, and made to turn aside horizontally when required; focussing and illumination were managed in the usual way, but there was a slow motion in addition to the rackwork. In offering the instrument for discussion, the question would arise as to the best form of lens to be employed, and he hoped to receive the opinions of the members upon this and other matters; but at present he used an ordinary low-power achromatic objective, made so as to slip into the arm without screwing; there was great convenience in thus mounting, and using a simple lens. With the old doublet there was much difficulty in working comfortably, and whether a person could do so or not depended a good deal upon his nose, being specially troublesome in the case of those persons who had somewhat aspiring noses. In addition to the lens which he had placed upon the instrument there was another belonging to it of half the focal length. Now, supposing they had made their dissection successfully, the point was how to be able to convert the instrument at once into a compound microscope without disturbing either the lens or the object. One of his aims in life had been to get microscope makers to abolish screws, which he regarded altogether as abominable inventions, and in this instance, the compound body had been made to slip over the outside of the socket in which the objective had been placed. This plan answered fairly well, but he thought it would be better to have it made to fit rather more easily, and to be secured by a bayonet joint, because, supposing that the power employed was not sufficient for the purpose, then inconvenience arose unless the body could be got off again with sufficient case to ensure the object remaining undisturbed by any jerk or movement. With the improvement of the bayonet joint, it would be easy to remove the body, and having taken out the first lens and dropped in, say a one-eighth in., the body would go on again without any disturbance. He had the instrument before them made upon that pattern, to see how the thing would work ; he had used it for the past six or eight months incessantly, and could certainly say that for his requirements it was the best thing he had seen, and he believed that with the little addition of a bayonet joint it would be as nearly perfect as any instrument of the kind could well be. He [318] thought that all persons who had been occupied in making minute dissections would see that it had value, and met all the requirements of the most delicate work. He hoped that the members would examine and criticise it, and make any suggestions that occurred to them for its further improvement, for it was becoming of very great importance to examine thin sections and minute portions of dissections without subjecting them to any disturbances as to cause the slightest alteration, and it was equally important to be able to bring to bear upon them under such conditions the highest powers that might be needed.
