. On microscopical manipulation : being the subject matter of a course of lectures delivered before the Quekett Microscopical Club, January-April, 1869. rs are abouthalf those of lenses of similar and double are also lenses convex on one surface, andconcave on the other; these are called meniscuslenses ; the curves may be so proportioned that theyhave either the power of convex or concave lenses,according as they are thickest in the middle or atthe edge; they have, moreover, some propertiespeculiar to themselves which are turned to goodaccount by skilful opticians. The formati
. On microscopical manipulation : being the subject matter of a course of lectures delivered before the Quekett Microscopical Club, January-April, 1869. rs are abouthalf those of lenses of similar and double are also lenses convex on one surface, andconcave on the other; these are called meniscuslenses ; the curves may be so proportioned that theyhave either the power of convex or concave lenses,according as they are thickest in the middle or atthe edge; they have, moreover, some propertiespeculiar to themselves which are turned to goodaccount by skilful opticians. The formation of images is one of the most valu-able properties of convex lenses, and one taken ad-vantage of in the construction of optical a convex lens is held at the distance of its focallength in front of a sheet of paper or other white sur-face, an inverted pidture more or less distinct will be 8 MICROSCOPICAL MANIPULATION. seen of objeas that may be before it, such as a windowor candle flame. This is illustrated by the diagramFig. 5, representing a candle flame on the left hand,from the apex of which two rays diverge, the lower Fig. one reaching the lower edge of the lens and theupper one its centre. Rays proceed from each pointof the flame to every part of the surface of the lens,but, for the sake of clearness, only two are here re-presented. After passing through the lens they con-verge ; the same takes place with the rays proceedingfrom the lower part of the flame, which also passthrough the lens. The result is the formation of an in-verted image, the size of which and its distance fromthe lens are dependent upon the distance of the objectand the focal length of the lens. The greater the distance of the objedl, or anteriorfocus, the shorter will be the distance of the image,or posterior focus. The commonest example maybe taken from the operations of the photographer,who, if he wants to take a small portrait, will placethe sitter at a great distance from the ca
Size: 3152px × 793px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1870, booksubjectmicroscopy, bookyear1
