SGS 



WELLS'S NATURAL PHILOSOPHY. 



screen, the larger the image will appear ; but when the distance is considera- 

 ble the image becomes indistinct. 



What are Dis- '^^S. The beautiful optical combinations 



BoivingViews? jjQown as Dlssolving Views are produced by 

 means of two magic lanterns of equal power, so placed as 

 to throw pictures of precisely equal magnitude on the 

 same part of the same screen. By gradually closing 

 the aperture of one lantern and opening that of the other, 

 a picture formed by the first may seem to be dissolved 

 away and changed into another. 



Thus, if the picture produced by one lantern represents a day landscape, 

 and the picture produced by the other the same landscape by night, the one 

 may be changed into the other so gradually as to imitate with great exactness 

 the appearance of approaching night. 



What is a Solar 'i^29. The Solar Microscope is an optical in- 

 Microscope? gtrument constructed on the principle of the 

 magic lantern, but the light which illuminates the object 

 is supplied by the sun instead of a lamp. 



This result is effected by admitting the rays of the sun into a darkened 

 room, through a lens placed in an aperture in a window shutter, the rays 



being received by a plane mirror fixed ob- 

 .liquely, outside the shutter, and thrown 

 horizontally on the lens. The object is 

 placed between this lens and another 

 smaller lens, as in the magic lantern ; and 

 the magnified imago formed is received upon 

 a screen. In Fig. 307, which represents 

 ihe construction of the solar microscope, 

 is a plane mirror, A the illuminating lens, 

 and B the magnifying lens. The objects to 

 be magnified are placed between the lenses A and B. In consequence of 

 the superior illumination of the object by the rays of the sun, it will bear to 

 be magnified much more highly than with the lantern. Hence this form of 

 microscope is often employed to represent, on a very enlarged scale, various 

 minute natural objects, such as animalculfc existing in various liquids, crys- 

 tallization of various salts, and the structure of vegetable substances. 



Pia. 307, 



