CAMERA LUCIDA 



1081 



CAMERON 



position, however, and anything visible in the 

 finder will appear in the photograph. In 

 nearly all types of cameras the shutter is 

 controlled by a spring, which may be released 

 by pressure on a lever or on a rubber bulb 

 which in turn releases the lever. 



Uses of the Camera. The camera is now 

 used in almost every art and industry. Photo- 

 engraving (which see) is perhaps its most 

 important commercial use, but there are dozens 

 of other processes and industries in which it 

 plays a part. Special cameras, both large and 

 small, are made for particular purposes. The 

 solar camera, for example, is used in connection 

 with a telescope to photograph stars and 

 planets not visible to the naked eye (see AS- 

 TRONOMY). At the other end of the scale are 

 cameras specially made for scientific research 

 with the microscope. Then there are the 

 multiplying camera, in which a number of 

 lenses are used for taking several pictures at 

 one time; the stereoscopic camera, a double 

 camera for giving a double picture on one 

 plate; the copying camera, used for copying 

 photographs from negatives; and the cyclo- 

 ramic camera, which turns on a central pivot 

 and takes a panoramic view at a single ex- 

 posure. One of the most remarkable kinds of 

 cameras is used for taking moving pictures. 

 This type of camera is fully explained in the 

 article MOVING PICTURE. For further details 

 of the use of cameras, see PHOTOGRAPHY, sub- 

 head Amateur Photography. K.A.G. 



CAM 'ERA LUCIDA, lu'sida, a simple in- 

 strument used for sketching objects seen 

 through a magnifying glass. It consists of a 

 four-sided prism, having two sides at right 

 angles, and the other two at an oblique angle, 



' at which 

 imaye a nen 



CAMERA LUCIDA 



'-Image of 

 object 



and a magnifying glass, both being attached to 

 a frame in the positions shown, in the illustra- 

 tion at the left. The light from the object 

 enters the prism and is reflected at a to the 

 point b, where it is reflected to the lens, 

 through which it passes to the eye. The magni- 

 fied image is thrown upon the paper where the 



sketch is made. Another form, shown at the 

 right in the illustration, uses a right-angled 

 prism with a sheet of glass for a reflector. 

 But the form first described is in most general 

 use. The camera lucida is used for sketching 

 parts of insects, the cell structure of plants and 

 other very small objects. It is seldom seen 

 outside biological laboratories. 



CAM 'ERA OBSCURA, obsku'ra, a box ar- 

 ranged for sketching landscapes and other large 

 objects. The box contains a mirror, a, set at 

 an angle of 45 ; a double-convex lens (see 

 LENS), such as is used in a photographic cam- 



\0bject 

 I- 



CAMERA OBSCURA 



era, is placed in the front end, and the top 

 has a lid which can be raised. Under the lid 

 is a ground glass screen. The image of the 

 object is formed on the mirror and reflected 

 upon the screen where it can easily be sketched 

 with a lead pencil. The instrument should be 

 used in a dark room, or a black cloth should 

 be thrown over it and the head and shoulders 

 of the one making the sketch, otherwise the 

 image will be too dim to admit of sketching. 



Before photography became so common, the 

 camera obscura was in general use by artists 

 in making sketches for illustrated papers and 

 magazines, but it is now seldom used except 

 as a toy. 



CAMERON, AGNES DEAN (1863-1912), a 

 Canadian educator, traveler and author, known 

 for her study of Canada's natural resources. 

 She was born in Victoria, B. C., where she 

 began teaching at the age of fifteen, and for 

 twenty-five years was closely identified with 

 the public schools of the province. During the 

 last ten years of her service she was principal 

 of the South Park public school, Victoria. In 

 1908 she traveled 10,000 miles, from Chicago to 

 the Arctic Ocean, by way of the Athabaska, 

 Slave and Mackenzie rivers, returning through 

 the Peace River Valley; this exploit gave her 

 fame as the first woman explorer to reach the 

 Arctic Circle. She was accompanied on this 

 rough adventure only by her niece. Miss 

 Cameron was for several years associate editor 

 of the Educational Journal of Western Canada, 

 made frequent appearances on the lecture plat- 



