22 I'lot'. llelmholta on the Telestercoscopa . 



iiicnt or not. All portions of the landscape that are not too 

 distant, assume the same bodily appearance as in the stereoscope, 

 and retain at the same time the whole richness of the natural 

 colours, so that images of surprising beauty and elegance are 

 obtained. 



Distant objects certainly appear flat, but still detach them- 

 selves from their background. Thus, for example, mountains 

 at two English miles distance detach themselves from the firma- 

 ment. As in the case of stereoscopic photographs, the aspect of 

 groups of trees is very surprising ; for the single boughs, and 

 the single twigs of each bough, detach themselves completely 

 from each other. Low clouds also appear frequently more solid, 

 and more separated from each other in the instrument, than 

 when regarded with the naked eye. 



The greater the distance between the two large mirrors, the 

 further in the distance does the instrument show the bodily form 

 of objects. Large reflectors give a large field of view. If there- 

 fore it is desired to fix the instrument so as to regard in it a 

 certain prospect, it will be advantageous to make the reflectors 

 as large as possible, their distance asunder a maximum, and to 

 j)lace the whole upon a table which admits of being turned. For 

 general purposes, it is convenient not to make the length of the 

 instrument greater than the width of a window, so that it may 

 be used from the room within. We obtain, moreover, a great 

 ])oition of the effect with small instruments, in which the di- 

 stance of the reflectors from each other is much less. 



Those who are accustomed to make optical experiments, 

 can obtain a telestereoscopic view of a landscape without any 

 other instrument than a small and a large mirror. The large 

 mirror is so suspended, that when looked into at an angle of 45° 

 the landscape is seen. The observer stands at a distance of some 

 feet from the mirror in this direction, and holds the small re- 

 flector parallel to the large one, opposite to the eye which is 

 nearest to the large mirror. For example, when the right side 

 of the obseiTcr is nearest the large mirror, the landscape in the 

 small mirror is to be regarded with the right eye, and in the 

 large mirror with the left eye. When both images are brought 

 to coincidence, the same optical efi'ect is obtained as in the tele- 

 stereoscope. Li this way, however, it is only with difficulty that 

 different ])arts of the view are successively united, and nearer 

 (jbjects appear to the left eye of less magnitude than to the 

 right one. 



To see near oi)jects in the telestercoscopc, the reflectors must 

 be turned round their vertical axes so that the angle between their 

 surfaces and the long edge of the box is somewhat greater than 

 45". The objects then appear greatly reduced in t<ize, but in 



