THE MUSEUM. 



55 



produces in glandular organs, some- 

 tiines arranged in bands or patches on 

 the surface of the sub-umbrella and 

 sometimes in circles at the base of the 

 peduncle. But these ova, when e.\- 

 cluded, produce creatures very differ- 

 ent from the parents and it is not till 

 the second generation that the original 

 Medusas is reproduced." 



The Medusa are very abundant 

 and the different species are scattered 

 throughout the seas though the tropi- 

 cal waters possess the greater num- 

 ber. Quantities are destroyed each 

 year by violent storms and other nat- 

 ural causes, the number taken by col- 

 loctors being e.xceedingly small in pro- 

 portion. They are of no special value 

 except to scientists and probably will 

 never be exterminated as some of the 

 other beautiful works of nature have 

 been. F. P. Drowne. 



X-Ray Photography- 



WILLIAM NEWELL. 



To many readers the above topic 

 may seem familiar. To all, doubt- 

 less, the greatest and most important 

 scientific discovery of recent yearr, 

 that of the X or Rontgen rays, is f:i- 

 miliar in many of its details. .'\c- 

 counts of the wonderful light that can 

 penetrate wood, flesh and even bone, 

 and the advantages gained to the med- 

 ical world thereby, have been herald- 

 ed far and wide by our newspapers 

 and periodicals. 



It would be superfluous to burden 

 our readers with detailed theories and 

 explanations of the Rontgen rays and 

 the Crookes tube with which they are 

 generated. We will therefore men- 

 tion only such as bear directly upon 

 our subject, i. e., x-ray photography, 

 or if it were more properly named 

 would be "shadowography," since the 

 photos are produced by shadows and 

 not in any case by a camera. 



The essential parts of the "x-ray 

 apparatus" which we must consider 

 are, first, the Crookes tube, an oblong 

 circular globe, not unlike that of an 



incandescent lamp, having within it at 

 one end a platinum or aluminum pole 

 and at a point about the middle of one 

 side a similar pole. Within the tube 

 there is no connection between the 

 poles but externally they are connect- 

 ed with the positive and negative poles 

 of a storage battery which supplies the 

 current. Between the battery and 

 tube the current passes through a re- 

 sistance coil increasing thereby the 

 voltage. The interior of the tube is 

 almost a perfect vacuum. The two 

 poles pass through the glass at the end 

 and sides, the glass besides being a 

 non-conductor, excluding all air. By 

 the passage of the electric current 

 from one pole to the other through 

 this vacuum the "x-rays" are produced 

 and are thrown off from the larger end 

 of the tube. Of course should the 

 current be reversed the rays would be 

 thrown in the opposite direction but 

 for present purposes we will suppose 

 them projected directly from the end 

 of the tube. 



The rays themselves are invisible to 

 the eye but if all other light be exclud- 

 ed from the room and a florescent 

 screen be placed a few inches from 

 the end of the tube so that the rays 

 I herefrom be thrown directly on an 

 object placed between the tube and 

 the screen will throw a shadow upon 

 the latter that can easily be seen from 

 the opposite side. If a hand be plac- 

 ed before the tube so that its shadow 

 will fall upon the screen, not only the 

 shadow of the hand will be seen, but 

 also the shadows of every bone there- 

 in, the bones giving a much heavier 

 shadow than the flesh. To show how 

 these shadows and impressions are 

 made permanent by photographic pro- 

 cesses, is the object of this article. 



A photographic dry-plate upon 

 which a negative of any object is 

 made consists essentially of a glass 

 plate upon which is an undecomposed 

 salt of silver. Briefly stated, the 

 making of a negative consists in al- 

 lowing decomposition of the silver salt 

 by exposure to light, the density in 



