. The silver sunbeam : a practical and theoretical text-book on sun drawing and photographic printing. rays. As a substitute, a very pure cobalt-blue glass may beused, which is easily placed on the plate of the it does not possess the same qualities as the so-lution of sulphate of copper, it is more practical. Such isthe opinion of Dr. Maddox, who is an incontestable au-thority on photomicrography. For the minor enlargements the manipulations do notpresent any serious obstacles; the lighting is easy and thequantity of light always suf-ficient. But when a power-ful objective
. The silver sunbeam : a practical and theoretical text-book on sun drawing and photographic printing. rays. As a substitute, a very pure cobalt-blue glass may beused, which is easily placed on the plate of the it does not possess the same qualities as the so-lution of sulphate of copper, it is more practical. Such isthe opinion of Dr. Maddox, who is an incontestable au-thority on photomicrography. For the minor enlargements the manipulations do notpresent any serious obstacles; the lighting is easy and thequantity of light always suf-ficient. But when a power-ful objective is made use of,the front lens of which isnot a millemetre in diam-eter, and on which the lu-minous rays, after their rec-tification by the cobalt glass,are condensed, there is agreat loss of intensity, especially when combined with alength of camera extended to two metres. It is necessary,then, to condense the solar light by means of several con-verging lenses placed upon its 468 PHOTOMICROGRAPHY. The great degree of enlargement obtained is the triumph ofphotomicrography. For obtaining this with clearness, objec- Fig 8. tives must be employedwherein the principleof correction is mostcarefully attended should be cor-rected beforehand foreach preparation, onaccount of the varyingthicknesses of the glasscovering used to pro-tect the object. It isby these precautions,and the improvementsmade by the construct-ors of instruments, thatwe are enabled to re-produce with clearnessthese powerfully-mag-nified specimens. Instead of obtainingdirectly a great en-largement, a cliche maybe taken with a weakobjective and enlargedby the processes gen-erally practiced. This method is very attractive, in conse-quence of its success in portraits, but does not succeed sowell with photomicrography. The infinite minuteness ofthe details requires no common precision, the least imper-fections assuming, in the enlargements, extraordinary pro-portions; and, further, the diffic
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