Apkil 24, 1896.] 



SCIENCE. 



635 



THE PREEOGATIVES OF A STATE GEOLOGIST. 



It was with surprise that I noticed in a re- 

 cent number of Science a communication on 

 the ' Prerogatives of a State Geologist, ' in 

 which I am made the target of considerable 

 unfair criticism. The temerity of its author, 

 Mr. Erasmus Ha worth, in distorting facts is not 

 only a little astonishing, but smacks almost 

 of deliberate endeavor to misrepresentation. 

 Ordinarily it would not demand the slightest 

 notice, but from the character of the presenta- 

 tion there might appear some plausibility to 

 some of those who have no personal knowledge 

 of the circumstances, of the animus of assault, 

 or of the persons involved. I do not care to 

 impose, even upon an indulgent public, an 

 account of the various dilierences which have 

 recently arisen between Mr. Haworth and my- 

 self. I only wish to make the statement, and 

 that emphatically, that the charges made are 

 either wholly false or are calculated to deceive. 

 With the same data and by the same adroit 

 manipulation of phrases and partial quotation 

 it can be proved to the full satisfaction of the 

 sunflower savant that the moon is made of 

 green cheese. Charles R. Keyes. 



COIN distortions by eontgen rays. 



We have repeated Professor Frost's interest- 

 ing experiments on the distortion of coins 

 (Science, N. S, Vol. III., No. 65, p. 465) in 

 skiagraphs, but we have come to the conclusion 

 that the distortion is due, not to electrostatic 

 charges (as was suggested in the article referred 

 to), but simply to umbras and penumbras 

 formed by rays emanating from different points 

 and falling upon coins of diflerent thicknesses. 

 In repeating Prof. Frost's experiments, we had 

 the Crookes tube 14 mm. above the silver dol- 

 lar and the film 3 mm. below the coins. We 

 then placed the coins on a horizontal pane of 

 glass and in the same position relative to the 

 Crookes tube above them as when the skiagraph 

 was taken. On holding a piece of paper up 

 against the pane and examining by the eye, from 

 below, the shadow cast by the coins in the light 

 of the Crookes tube above, the very same dis- 

 tortion was seen that was shown in the skia- 

 graph. 



With the view of preventing X-rays having a 

 large incident angle from striking the edges of 

 the coins forming the curvilinear triangle, we 

 placed upon the triangle a cylindrical section 

 cut from the neck of a yellow-glass bottle. The 

 section was ground down to a height of 11 

 mm., its internal diameter varied from 13 to 

 15 mm., its thickness was 5 mm. The distor- 

 tion in the skiagraph was a trifle less than for- 

 merly, but more pronounced, we thought, than 

 in the ocular test. 



Fearing that the glass was somewhat trans- 

 parent to X-rays, we replaced it by three iron 

 washers superposed upon each other. Their 

 internal and external diameters were 14 mm. 

 and 34 mm. respectively, and their combined 

 thickness was 9 mm. The tube, film and coins 

 were in the same relative position as before. 

 The skiagraph revealed much less distortion 

 than in the first exposure. The ocular test 

 with the washers on and with them off pro- 

 duced, as nearly as we could tell, exactly the 

 same effects as were shown in the skiagraphs. 



In another trial we discarded the washers 

 and separated the coins from the film by only 

 three thicknesses of black paper. The tube 

 was again 14 mm. above the coins. As expected, 

 the edges of the coins in the skiagraph were 

 very sharp, and there was no trp,ce of distor- 

 tion. In this case the electrostatic charges 

 must have been fully as pronounced as in the 

 first experiment, but a perceptible penumbra 

 could not have been formed. It would seem, 

 therefore, that the distortion was due simply to 

 umbras and penumbras cast by the coins. 

 Florian Cajori, 

 William Strieby. 



Colorado College, 



April 10, 1896. 



SCIENTIFIC LITER ATUBE. 

 the eruptive sequence. 

 Die Eruptivgesteine des Kristianiagebietes II. 

 Die Eruptionsfolge der triadischen Eruptivges- 

 teine bei Predazzo in Siidtyrol. Von Dr. W. 

 C. Brogger. Videnskabsselskabets Skrifter, 

 I. Mathematisk-Naturv. Klasse. 1895, No. 

 7. Kristiania. 

 After many years of exhaustive research 



