192 



SCIENCE 



[N. S. Vol. XXXVII. No. i 



The section consists of alternating slate and 

 gray sandstone layers, of a few feet thickness. 

 The slate usually has numerous fossil plant 

 impressions in it, but the sandstone here is 

 barren of recognizable organic remains. 



The specimens of the genus Leaia Jones, 

 are in general well preserved and show the 

 surface markings distinctly (see Fig. 1). 



F,c.Z. 



X2. 



They correspond closely with the description 

 and figures of Leaia tricarinata Meek and 

 Worthen," of the Illinois and Indiana Coal 

 Measures. The size of an average specimen 

 from Ehode Island is : length, 8.5 mm. ; height, 

 5 mm. The presence of a well-marked third 

 carina along the dorsal margin and the twelve 

 to sixteen slender concentric ridges, as well as 

 the agreement in size, make it seem safe to 

 call the Ehode Island specimens Leaia tri- 

 carinata. 



Several specimens of the genus Estheria 

 Ruppel occur in the same layer with Leaia 

 (see Kg. 2). They vary slightly in size and 

 proportions, but all show the generic charac- 

 ters well. The surface markings are not as 

 distinct as in the specimens of L. tricarinata, 

 but most of the Estheria specimens show from 

 nine to thirteen faint concentric striae. The 

 size of an average specimen from Rhode 

 Island is : length, 7 mm. ; height, 5 mm. The 

 specimens are not sufficiently well preserved to 

 permit of a specific determination. 



In the Conemaugh Series of the Carbon- 

 iferous of Pennsylvania, Dr. P. E. Eaymond' 

 has noted the presence of Estheria and Leaia 

 tricarinata, with plant remains, in a red and 

 gray shale layer occurring just below the 

 Ames limestone, which is midway in the Cone- 

 maugh Series. Fossils of the two genera 

 occur in several horizons of the Coal Measures. 

 In niinois L. tricarinata ranges from the 



• Geol. Surv. III., Vol. 3, pp. 541-543. 

 'Ann. Carnegie Mus., Vol. V., No. 2 and 3, 

 1909, p. 173. 



lower part of the Lower True Coal Measures, 

 to high up in the Upper Coal Measures, there- 

 fore neither genus is a good horizon marker. 

 If we regard the Estheria, L. tricarinata hori- 

 zon of the Conemaugh Series as of the same 

 age as that at Central Falls, E. I., we should 

 then be calling this horizon of the Narragan- 

 sett Basin Series the equivalent of the middle 

 of the Lower Barren Measures of Middle Penn- 

 sylvanian age. Winthrop P. Hayjjes 



Cambridge, Mass., 

 October, 1912 



THE ELECTROMOTIVE FORCE PRODUCED BY THE 

 ACCELERATION OF CONDUCTORS 



The possibility that electromotive forces 

 may be produced by the mechanical accelera- 

 tion of electric conductors was first thoroughly 

 considered by Maxwell,' and the actual pres- 

 ence of such electromotive forces in electro- 

 lytic conductors was shown by Colley" in 1882. 



The desirability of obtaining similar electro- 

 motive forces in accelerated metallic conduct- 

 ors has long been recognized by the writer. 

 At a meeting of the Harvard and Massachu- 

 setts Institute of Technology Physical Chem- 

 ical Society, held at the Harvard Union in the 

 spring of 1906, he stated that a potential differ- 

 ence was to be expected between the front and 

 rear ends of a metallic conductor which is 

 suddenly stopped, since there will be a tend- 

 ency for the electrons to continue in motion. 

 Since that time he has often spoken to his col- 

 leagues, both privately and at informal scien- 

 tific meetings, of the desirability of making 

 measurements of this kind in order to obtain 

 information as to the mass of the carrier in 

 metals, and in particular has described as a 

 possible form of apparatus a coil of wire os- 

 cillating about its own axis with some form 

 of commutator to permit the detection with an 

 ordinary galvanometer of the alternating cur- 

 rent which would be generated. 



During the past year at the University of 

 Cincinnati, with the help of his assistant, Mr. 

 Earl W. Osgerby, the writer has carried out 



' Maxwell, ' ' Treatise on Electricity and Mag- 

 netism," 3d edition (1892), Vol. II., 211 at seq. 

 'Colley, Wied. Ann., 17, p. 55, 1882. 



