EARLY BINOCULAR MICROSCOPE 131 



applicable to both eyes at once ; a segment of each object-lens 

 (supposed to be of one-inch focus) was ground away to allow the 

 convergent axes starting from the two eyes to meet at about 16 

 inches distance at the common focus. Mechanism was provided for 

 regulating the width of the axes to correspond with the observer's eyes. 



Fig. 97, showing the optical construction, is copied from the 

 original diagram (' La Vision Parfaite,' tab. i. fig. 2, p. 80). Accord- 

 ing to the arrangement of the lenses as shown in the figure a pseudo- 

 stereoscopic image would have been obtained. 



A drawing of this binocular, as known to Zahn, was given in 

 the first edition of his ' Oculus Artificialis ' in 1685 (Fundamen III. 

 p. 233), and is reproduced in fig. 98. 



K 2 



