140 MANAGEMENT OF THE MICROSCOPE. 



wants of the Microscopist. Thus, although a wax or composition 

 Candle affords a very pure light, yet its use is attended with 

 two inconveniences, • which render it very unsuitable when any 

 better light can be obtained : — namely, the constant flickering of 

 the flame, which is not, sufiiciently prevented by surrounding it 

 with a chimney ; and the continual alteration in its level, which is 

 occasioned by the consumption of the candle. The most useful 

 light for ordinary use is that furnished by the steady and constant 

 flame of a Lamp, fed either with Oil, Camphine, Paraffine (of its 

 best varieties) or Gas ; it should be capable of adjustment to any 

 height above the table ; and a movable shade should be provided, 

 by which the light may be prevented from coming direct to the 

 observer's eyes, or from diffusing itself too widely through the 

 room. These requisites are supplied by the Lamp commonly known 

 as the ' University ' 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 be fixed at any convenient height. 

 French and German lamps, on the same general construction, but 

 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 ; and they are now 

 made with shades, well suited to the wants of the Microscopist.* 

 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. Small Camphine lamps are now constructed for 

 the special use of Microscopists, which are capable of being placed 

 on an adjustable stand, so that their 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 (§ 87) ; 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. The Paraffine or Belmontine 

 lamps, which have latterly come into such general use, have many 

 advantages for the Microscopist ; and are probably, on the whole, 

 when constructed with express reference to his requirements, the 

 most convenient lamps he can employ. The Author can strongly 

 recommend, from his own experience of its use, the form known 

 as the Bockett Lamp (Fig. 85), manufactured by Mr. Collins. 

 This is attached by a transverse arm to a tubular slide, which 

 moves up and down upon the stem that rises from the foot, and 

 can be fixed by a milled-head ; and this slide also carries the Con- 

 * A very excellent Lamp of this kind is sold by Mr. Pillischer. 



