156 MANAGEMENT OF THE MICROSCOPE. 



or " reading" lamp, which has a circular foot with a vertical 

 stem, on which the oil-reservoir (carrying with it the burner) and 

 the shade, can he fixed at any convenient height. French and 

 German lamps on the same general construction, hut having the 

 reservoir contrived on the " bird-fountain" principle, are also to 

 be obtained, being largely imported for the use of watch-makers ; 

 these have the advantage of burning out all their oil, which is 

 not the case with the ordinary " reading"-lamp, as it does not 

 burn well except when full or nearly so ; but they are usually 

 destitute of a shade, which, however, can be easily added. 

 Lamps of either kind are sometimes constructed on the " solar" 

 principle, which increases the purity and intensity of the light, 

 but at the same time not only diminishes the diameter of the 

 flame, but also produces an inconvenient transverse "break" 

 near its lower part. The best kind of light which an oil-lamp 

 can furnish, is that yielded by the "Moderator" lamps which 

 have of late come into such general use ; but they have this im- 

 portant drawback, that they contain in themselves no adjustment 

 for var^'ing the elevation of the burner, and that their construc- 

 tion is such as to give no facilities for any arrangement of this 

 kind. The same objection applies to the Camphine-lamps in 

 ordinary use ; but a small camphine-lamp has been constructed 

 for the special use of Microscopists, which is capable of being 

 placed on an adjustable stand, so that its flame may be raised or 

 lowered to any desired level. The light of this lamp is whiter 

 and more intense than that of any other, and it may be used with 

 advantage for certain very delicate observations (§ 68) ; but for 

 the ordinary purposes of the Microscopist it is not so convenient, 

 the surface of flame from which the light can be received by the 

 mirror or condenser, being limited by the peculiar construction 

 which the combustion of camphine requires. To every one who 

 has a supply of gas at command, the use of it for his microscope- 

 lamp (by means of a flexible tube) strongly recommends itself, 

 on account of its extreme convenience, and its freedom from any 

 kind of trouble. The lamp should be constructed on the general 

 plan already described, the burner being made to slide up and 

 down on a stem rising perpendicularly from a foot, which also 

 carries a shade ; and the burner should be one which aftbrds a 

 , bright and steady cylindrical flame, either " Leslie's" or the 

 " cone"-burner being probably the best. Even the best light 

 supplied by a gas-lamp, however, is inferior in quality to that of 

 a good oil-lamp ; and is more injurious and unpleasant to the 

 eye. Hence the interposition of some kind of artificial medium, 

 adapted to keep back the yellow rays, whose predominance in 

 the lamp-flame is the chief source of its injurious action, is es- 

 pecially required when gas-light is used. This may be partly 

 efi'ected, by the simple expedient of using a chimney of bluish 

 glass, known as " Leblond's ;" but, in addition, it is advantageous 

 to cause the light to pass through a screen of bluish-black or 



