374 THE AMERICAN MONTHLY [Dec 



being squared with a simple and conveniently adjustable 

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

 ohtained, the two arms of the fluorometer will present 

 the characteristic single shadow on the field of the fluoro- 

 sc.>iie. 



Attachable to the arms of the fluorometer are two pins 

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

 iia\ iiig been brought in line with them and the proper 

 adjustment having been made, a correct line is produced, 

 with the sights and foreign object coincident. By means 

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

 jiceiit to one side of the body and consequently one side 

 of tlie fluorometer, exact measurments can be made with 

 I lie 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 

 ( lookes tube is placed directly over the subject for the 

 piir[)0se of obtaining the vertical line. By means of an 

 adjustable cross-piece, which is placed over the arms, 

 exact ly the same results in a vertical way are obtained 

 by viewing the subject from beneath, the same condition 

 oT parallelism having been produced, another set of pins 

 having been placed in position. 



Wiiile the first operation locates the foreign object on 

 un 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- 



