62 THE SALMON FLY. 



lamp and reflector slides up and down on the pillar, and is secured at the desired 

 height by a thumbscrew. The carrier of the lamp and reflector is attached to this 

 fitting by a knuckle joint, so that it can be inclined to the angle required for 

 directing the light on the object. Another thumbscrew tightens and fixes this 

 joint when the angle is once adjusted. The wire from the fitting of the wall plug 

 is carried to the lamp in the ordinary way, and is of sufficient length to enable the 

 stand to be moved on the table as required. The source of light is an ordinary 

 eight-candle incandescent ground glass lamp, and for convenience of lighting or 

 extinguishing without connecting to or disconnecting from the wall plug, has an 

 independent switch fixed to the carrier. The reflector, also of bronze, with the 

 interior or reflecting surface heavily plated and polished, has a true parabolic 

 figure. The eight-candle lamp is placed in the carrier, so that as near as possible 

 the source of light is at the focal point of the paraboloid. . Scientifically, a light 

 thus placed is reflected in parallel rays of equal intensity in the direction of the 

 axis of the paraboloid, but this would only be possible if the source of light was a 

 geometrical point, and any increase of the area of the light produces bundles of 

 rays originating at various angles, and hence diverging and converging. This is 

 mentioned to prevent confusion, as it is impossible for an apparatus of this 

 description to be made so that all the rays are parallel, and the disc of light of 

 equal intensity throughout. 



" This arrangement carries out all the requirements laid down in the earlier 

 portions of this article. The light is sufficient to illuminate, and yet modified by 

 the ground glass of the bulb so as to be pleasant. By raising or lowering and 

 inclining to the requisite angle, the light can be directed on to the object with the 

 reflector at such a distance from the vice as to be quite out of the way. If all is 

 properly adjusted, the light itself is invisible to the worker, and none of the rays 

 are reflected into his eyes. The area of the table illuminated is also sufficient to 

 enable him to find any materials or implements he may require for his work. The 

 heat given off by electric light is much less than by any other illuminant known, 

 and is certainly not enough to cause any serious inconvenience to the operator. 

 Some readers may pertinently inquire what substitute can be suggested where 

 the modern improvement of electric light is not available. The answer is that a 

 paraffin or colza lamp, or an ordinary candle, can be fitted in a very similar 

 manner, but the distance of the lamp from the vice must be accurately determined, 

 and the angle at which the axis of the paraboloid should be inclined from the 

 perpendicular calculated, and the reflector fixed accordingly. It would not do to 

 fit the reflector on a knuckle joint, as when the inclination was varied the lamp or 

 candle would not be perpendicular, and hence would not burn satisfactorily. If 

 the light from the lamp or candle should be too intense, it could be modified by 

 the interposition of ground or coloured glass, or a bottle containing the mono- 

 chromatic fluid described above between the reflector and the object." 



