ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 505 



darkness of the room, and is able to distinguish objects much more 

 readily than at first. This is a principle which can be utilised to very- 

 great advantage in connection with high-power Microscope work. In 

 fact, the writer is of opinion that it is this contrast between the ex- 

 ternal and internal illumination which leads so many operators to use 

 artificial light, and even in some cases to prefer working in the evening. 

 Certain it is that if the surrounding light is dim, and the eye is allowed 

 to adjust itself to this dimness, then on looking through the Microscope 

 details may be seen much more clearly than in any other way. With 

 the present apparatus the room is darkened. All light which could 

 possibly get to the operator's eye is excluded, except that which comes 

 through the Microscope. There is no light coming upon the top of his 

 object to cause confusing reflections in the Microscope. The image is 

 as clear as it can be made, and the eye is given every facility to see this 

 image, and is distracted by no others. The following contrivances are 

 such as experience has shown the writer to be very useful for this pur- 

 pose, especially in sunny climates. Outside of the Microscope window a 

 universally adjustable white screen is placed in a sunny position, pre- 

 ferably not more than 10 ft. away. The surface of this screen may be 

 of any white material. It can be made of wood, painted white, or lined 

 with plaster of Paris, or, what to the writer seems almost equally good, 

 a plain wooden screen covered with several thicknesses of bleached cotton 

 cloth. It is better if this screen can be adjusted from the interior of 

 the Microscope room, but this is not essential. If a small mirror be 

 attached to the screen, it will indicate the position of the screen that 

 will reflect to the Microscope mirror a maximum of white light. Place 

 the screen so that the flash of sunlight from the mirror strikes in the 

 vicinity of the Microscope. Then, of course, the whole of the screen 

 will be in a corresponding position, and will be reflecting a maximum of 

 fight. It is found that if the screen be placed in this position for several 

 hours, the light from it remains practically constant, so that while an 

 adjustment by cords from the interior is a convenience, it is not a very 

 great necessity. If an adjustable screen is not available, it is generally 

 best to arrange one or two fixed screens, and thus accomplish the same 

 object — one screen for morning, and another for afternoon. The light 

 from a blue sky is not a satisfactory light. A white cloud gives a very 

 good light, but clouds are such fickle things that it is not wise to rely 

 upon them where the Microscope is in constant use. It is much pre- 

 ferable to construct a screen that will be available in a fixed position 

 whenever the sun shines. When the sun does not shine the sky must 

 serve. 



CAMERA LUCIDA FOR NATURAL SIZE OR REDUCED DRAWING. 



Ever since the introduction of the camera lucida, it has been 

 more or less used for the production of natural size and reduced 

 drawings ; in other words, it was soon seen that its application went 

 beyond the instrument for which it was primarily designed. The writer 

 has used the camera lucida to a greater or less extent in this manner 

 for twenty-five years, and has seen plenty of evidence that others have 



Aug. 15th, 1906 2 l 



