ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 721 



figure of the stellate liairs of Deutzia scahra, as imaged by reflected 

 light. Some of the plates when compared with silver prints rather 

 lack their brilliancy, yet still show the value of the method adopted. 



The book will, we have no doubt, prove very useful to the student, 

 especially now that photomicrography appears to be coming into 

 favour for illustrations. 



Photomicrography by Lamplight. — Dr. C. Kiaer, although his 

 process is nearly the same as that described by Mr. (x. M. Giles,* 

 thinks it may be useful to describe the advantages and defects which 

 lamplight, according to his experience, has in comparison with sun- 

 light. Dry bromsilver-gelatine plates were used. He formerly tried to 

 use lamplight on wet collodion-plates but without satisfactory result, 

 even with the lowest objectives. The feeble light necessarily demands 

 a much longer time for exposure than sunlight. The wet collodion 

 plates are too little sensitive for lamplight and dry up before the 

 necessary time has expired. The bromsilver-gelatine plates are 

 much more sensitive, so that the time for exposure may be shortened 

 to one-third or one-eighth of the time necessary for the wet plates. 



To develope the negative he uses a mixture of a solution of neutral 

 oxalate of potassium with a solution of protosulphate of iron with a 

 few drops of sulphuric acid. 



The lamp was a petroleum lamp, with a " sun-burner." The round 

 wick has a diameter of 25 mm., and the centre of the flame is elevated 

 about 22 cm. over the base of the apparatus. The lamp is placed 

 close to the (Nachet) Microscope, the latter being in an oblique posi- 

 tion about 30° from the vertical. This is preferable because the 

 focusing of the Microscope is more convenient, and because the 

 horizontal position would not permit the use of the concave mirror of 

 the Microscope. The distance between the flame and the mirror is 

 16 cm., and between the two is a biconvex lens of 8-9 cm. focus, 

 and 5i cm. diameter. The distance of the object from the ground 

 glass was always J m. With Nachet objectives No. and No. 1, the 

 plane mirror should be used, and with No. 5 the concave mirror. 



As the lamp produces a light of constant intensity it is easy after a 

 few trials to fix the exact time of exposure for each objective. For objec- 

 tive No. the proper time for exposure (without lens and wdth plane 

 mirror) is 9 minutes ; for objective No. 1., with lens and plane mirror, 

 3^ minutes for more transparent, and 7 to 10 minutes for yellow to 

 brown coloured objects ; for objective No. 5, vsdth only concave 

 mirror, 30 minutes; with lens and concave mirror, according to the 

 transparency of the object, from 7 to 15 minutes. 



During exposure, the whole apparatus must stand entirely un- 

 moved. Incautious walking in the room or the shaking produced by 

 a passing vehicle is deleterious. To make the apparatus more steady 

 the coarse adjustment should be screwed down. 



It was formerly very difficult to photograph yellow and hrown 

 coloured objects by sunlight vrith collodion plates, because these colours 

 act very slowly upon the plates. But when the bromsilver plates 

 are exposed (for double the time) the result is very satisfactory. 

 * Mon. Micr. Jouru., xv. (1876). 



