OF THE 3UCKOSCOPE. 155 



would be refracted to the point, h, if continued in solid glass, 

 but by impinging on the inclined polished surface (which is 

 far within the angle of total reflection), they are thrown on the 

 flat segmental top ; here they would be totally reflected and 

 beaten down again to a point outside the cylinder, but if an 



Fig. 46. 



object-slide, c, be laid over the flat top with an intervening 

 film of water, the rays will proceed on to the point, g, if the 

 glass slide be thick enough. As shown in the engraving, how- 

 ever, the slide is of the usual thickness, and the point, g, lies 

 above it ; therefore, if the upper surface of the slide is clean 



