374 THE AMERICAN MONTHLY [Dec 



being squared with a simple and conveniently adjustable 

 table. When the proper position of the cross-section is 

 obtained, the two arms of the fluorometer will present 

 the characteristic single shadow on the field of the fluoro- 

 sc.>i)e. 



Attachable to the arms of the fluorometer are two pins 

 or sights. By means of these sights, the foreign object 

 having been brought in line with them and the proper 

 fidjustment having been made, a correct line is produced, 

 with the sights and foreign object coincident. By means 

 of n metallic grating, of inch mesh, which is placed ad- 

 jacent to one side of the body and consequently one side 

 of the fluorometer, exact measurments can be made with 

 the eye from the base line, and from points on the cir- 

 cumference of the body, to the foreign object. 



Then, without moving the body or the fluorometer, the 

 Crookes tube is placed directly over the subject for the 

 purpose of obtaining the vertical line. By means of an 

 atlj'.istable cross-piece, which is placed over the arms, 

 exactly the same results in a vertical way are obtained 

 by viewing the subject from beneath, the same condition 

 of parallelism having been produced, another set of pins 

 having been placed in position. 



While the first operation locates the foreign object on 

 an exact cross-section, the second observation shows the 

 exact position occupied by the foreign object in that 

 cross section. All the elements of distortion having 

 been eliminated, the foreign body will necessarily be at 

 the intersection of the two lines of the right angle. The 

 first cross-section obtained is shown by a line of India 

 ink or iodine on the body. 



Very early in the history of the X-ray it was found 

 that it was a very deceptive guide, and that^ wherever a 

 a foreign substance which was less permeable than its 

 surroundings might be, it was certainly not in the posi- 

 tion indicated by the so-called radiographs or skia- 



