350 THE AMERICAN MONTHLY [Nov 



inches mip^ht be seen to consist of sixteen or seventeen 

 stars in line, almost touching one anotlier when seen 

 through the Lick photographic objective. A star appar- 

 ently single when seen through any objective, having an 

 aperture of three inches and three-quarters might be 

 seen to consist of eight or nine stars in line, almost touch- 

 ing one another, when seen through the Lick photo- 

 j^raphic objective. The power of resolving an apparent 

 single star into two or more, or of showing the details of 

 sun spots or other objects, is known as separating power. 

 A superior correction of aberrations is now possible in 

 lenses made of small discs of glass which are produced in 

 great variety as to optical properties, a variety not yet 

 realised, in large discs. — Tr. A. M. S. 



Progress in Effects with the Roentgen X-Rays. 



To see through a person in a metaphorical sense has 

 been the wish of most people at some time or another, 

 but it has now become a literal fact by means of the 

 occult rays, popularly known as the X-rays (on account 

 of their exact properties not being understood), discov- 

 ered by Professor Roentgen of the University of Wurz- 

 burg. It seems inexplicable that with the art of photo- 

 graphy, so highly developed as it has been for many 

 years, and with the experiments that have been taking 

 place in laboratories all over the world in radiant matter 

 in vacuum tubes, that we should have had to wait for tlie 

 year 1896 for this discovery to have l)een made practi- 

 cally available ; it only leads us to reflect that " there are 

 more things in heaven and cartli than arc dr«'amt of in 

 oar philosophy," and that there is yet room for fresh and 

 startling inventions and discoveries. 



The first announcement of Prof. Roentgen's discovery 

 that rays fron^ a Crooke's or Lennard's tube of high 

 vacuum had a power of penetrating numerous substances, 



