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THE AQUARIUM, APEIL, 1896. 



chamber of the camera, where it is 

 fixed ; whereas, in the process by 

 Roentgen light, no lens or camera is 

 necessary. A sensitive dry plate, such 

 as is used for instantaneous process 

 in ordinary photography, is carefully 

 wrapped in black paper to protect it 

 against the daylight. The object which 

 is to be photographed is simply placed 

 upon the plate thus prepared and ex- 

 posed for a longer or shorter duration, 

 according to the nature of the object, 

 to the X rays, as this light is called. 

 These rays are produced by the dis- 

 charge of a high potential electric cur- 

 rent, in a so-called vacuum tube, which 

 is a small air-tight glass cylinder, about 

 five inches long and one inch in diam- 

 eter, from which the air has been ex- 

 hausted. As soon as the current is 

 started the interior of the tube seems 

 to be filled with a greenish-yellow light 

 which accompanies, or, as some physi- 

 cists think, is the source of the X rays. 

 These rays, although very powerful, 

 are not visible either in a darkened 

 room or in daylight, but will pass 

 through many substances which are 

 opaque to ordinary light. 



In this case the salamander was set 

 upon a black cardboard ; this was placed 

 on top of the wrapped dry plate and 

 then exposed, at a distance of about 

 eight inches, to the action of the rays 

 for about twenty minutes. After this 

 the plate was taken to the dark room 

 and develojjed in the same manner as 

 any other exposed plate. After devel- 

 opment the negative showed the form 

 and natural size of the salamander as a 

 dark shadow, while the entire skeleton 

 appeared in white. Nothing was visi- 

 ble of the cardboard. 



The accompanying line drawing is a 

 correct reproduction of it. 



Together with the salamander (of 



course on different plates), the pictures 

 of a frog with a broken hind leg and 

 that of a young turtle were taken. 

 The break of the bone in the frog 

 could be plainly seen on the picture 

 thus produced ; and so was the picture 

 of the turtle quite a success, although 

 it had walked off the plate once. The 

 structure of its skeleton was plainly 



shown. 



— —* 



THE GOLDEN TENCH. 



( Tinea aui'eus. ) 



One of the many missions the aqua- 

 rium has to fulfill, is that of resting 

 the nerves. But it stands to reason, 

 that when an aquarium is expected to 

 spread a feeling of peaceable quiet and 

 contentment around us, an effect which 

 is so beneficial to invalids or aged 

 people and for overworked business 

 men, that we should select such speci- 

 mens for our collection as are through 

 the traits, peculiar to their race, best 

 fitted to accomplish that end. 



In the tench, the Green as Avell as 

 the Golden, we have a fish that pos- 

 sesses all the qualities required to pro- 

 duce the desired effect. The tench 

 seems to have been created for the pur- 

 pose of spreading salvation over the 

 entire finny tribe. Its character is 

 absolutely peaceable ; its manners are 

 modest, but by no means cowardly. It 

 is not at all particular in regard to its 

 food, thriving well on the ordinary, 

 easily obtainable foods used for other 

 aquarium fish. It becomes soon accus- 

 tomed to its master., and then prefers 

 to take its meals from his or her hand. 

 This sign of confidence especially has 

 a wonderful soothing effect upon most 

 people. 



At the present time we possess two 

 specimens of the Golden Tench, in dif- 



