144 SELECTION AND USE 



light reflected from a white wall, or a light fleecy cloud. Sun- 

 light is something which we cannot command at will, and, there- 

 fore, the microscopist can do nothing more than select the lo- 

 cation of the room which he occupies. In general a room with 

 a northern aspect is to be preferred; if there should also be 

 windows looking towards the east or west, so much the better, 

 provided they can be completely darkened when not in use, as 

 cross lights produce a bad effect. 



Artificial Light. While good daylight is the best source 

 of illumination, poor daylight is one of the worst, and we have 

 frequently, during the day, obtained by the use of lamps and 

 candles, results which could not possibly be secured by natural 

 daylight. At the present time, gas-light, lamp-light and can- 

 dle light are the most available means of artificial illumination. 

 Candles are rarely used except when the microscopist is travel- 

 ing, or in a peculiar situation, but a good candle gives very fair 

 results, especially if the flame be protected from currents 

 of air, which may easily be done by extemporizing a 

 shade out of a piece of glass tube or small lamp chim- 

 ney. Wax, paraffine or sperm candles should be chosen, as 

 they give a clear, white flame. Common tallow candles give a 

 dull yellow flame of inferior quality. Gas-light, as obtained 

 from the ordinary, flat, unprotected burner, is not sufficiently 

 steady; it flickers and changes, and for microscopy this is the 

 worst fault that an artificial light can have. Where gas is em- 

 ployed it is, therefore, necessary to use an argand burner, with 

 a glass chimney. Light obtained in this way is in general 

 very excellent. But the most convenient, as well as the best 

 means of illumination, is a good lamp, of which the ordinary 

 student's lamp is, on the whole, perhaps the best kind. It 

 gives a pure^steady and intense light; it is easily regulated, 

 both as regards brightness, and also position, and conse- 

 quently direction, and it may easily be procured almost any- 

 where. In default of a good student's lamp, any of the ordi- 

 nary lamps with circular, or flat wicks, may be made to answer. 

 Where a large quantity of light is required, as in the illumina* 

 tion of large opaque objects, the circular, hollow wick, from 

 the superior brightness and whiteness of the Hght ? is always to 



