April 28, 1905.] 



SCIENCE. 



665 



To understand the theory of the instrument 

 assume the lower bulb replaced by a continua- 

 tion of the barometer tubing of equal volume. 

 Let h stand for the standard barometer height, 

 m for the length of the thread of mercury 

 entering the tube, and a for the length of the 

 column of compressed air. Then from Bojde's 

 law (pv = p'v') we have 



6 ( a + m ) = (6 + wi ) a, 

 6 = a, 



and hence 



Ab = Ao. 



That is, the divisions of the scale on the Piezic 

 barometer are of the same size as those on 

 the ordinary barometer. However, in prac- 

 tise the upper bulb always contains some mer- 

 cury after the air is entrapped. The general 

 effect of this is to make Aa < 



The Exhibit of the U. S. Geological Survey 

 Radium Collection shown at the St. Louis 

 Exposition: G. F. KuNZ. 

 Mr. Kunz described the object of and the 

 success of the exhibit, stating that many of 

 the most eminent investigators, including Sir 

 William Crookes and Professor Rutherford, 

 had sent their original material. The collec- 

 tion was shown in an upi)er hall of the mtiseum. 

 There was also exhibited the Kunz 1,081-pound 

 mass of Canon Diablo meteoric iron, the 

 largest mass known of this meteoric iron. Mr. 

 Kunz stated that Professor Henri Moissan, of 

 Paris, had discovered in dissolving 183 pounds 

 of this material (Canon Diablo meteorite), 

 not only crystalline diamonds, but the crystal- 

 line substance, carbon silicide, never before 

 discovered as a natural product, but exten- 

 sively manufactured and used in the arts 

 under the name of carborundum. In view of 

 the many eminent discoveries of Professor 

 Moissan in the field of chemistry and electro- 

 metallurgy, as well as in the study of meteor- 

 ites and of diamond formation, Mr. Kunz 

 suggested that this mineral be named mois- 

 sanite in his honor. 



Experimental Research concerning Indirect 

 and Secondary Skiagraphic Rays: L. G. 

 Cole. 



The immediate discharge from an X-ray 

 tube consists of two distinct classes of so- 



called rays — direct and indirect. The direct 

 rays have their inception at the focal point of 

 the anode and radiate in direct lines and are 

 not reflected, but deflected, and do not set up 

 secondary rays, but are absorbed by the tissue 

 of the body in proportion to the amount of 

 solids contained therein. 



The indirect rays radiate from the walls of 

 the tube, are projected at various angles, and 

 cause secondary rays in objects with which 

 they come in contact, especially the soft tissue, 

 and give great penetration. The effect at- 

 tained depends on the amount of current, fre- 

 quency of interruption and molecular action 

 of glass. 



Dr. Cole then described the life history of 

 a tube, stating that definite changes occur in 

 a tube when used, including a crisis, and ex- 

 plained the difference between the action of 

 new and seasoned tubes and the difficulty of 

 exciting very old tubes. 



He also gave his opinion of the cause of the 

 purple color of the glass of a tube and sug- 

 gested that there is a molecular rearrangement 

 of glass similar to that occurring in steel when 

 magnetized. In a new tube the direct rays 

 amount to 30 to 40 per cent., while in some 

 seasoned tubes as much as 75 to 90 per cent. 

 Furthermore, the indirect rays pi'oject them- 

 selves behind the bones, causing a lack of defi- 

 nition of bones and obliteration of detail of 

 soft parts, while direct rays give detail in soft 

 parts, showing even the blood in the veins. 



Dr. Cole, who is skiagrapher at Roosevelt 

 Hospital, will publish his paper in full in the 

 Archives of the Rontgen Ray Magazine. 



C. C. Trowbridge, 



Secretary. 



THE science club OF THE UNR^ERSITY OF 

 WISCONSIN. 



The sixth meeting of the club for the year 

 1904-5 was held on Tuesday, March 21, at 

 7 :30 p.jr. in the physical lecture room, Sci- 

 ence Hall. 



The first paper on the program, by Dr. R. 

 Fischer, treated the subject ' Food Adultera- 

 tions and their Detection.' The various 

 methods of adulteration of human foods met 

 with this state, and the methods of their 



