232 Intelligence and Miscellaneous Articles* 



in rocks of the Chemung group. It is a fragment of a well-charac- 

 terized stem, with parts of five petioles attached to it, and asso- 

 ciated with remains of the leaves. It must have been entombed in 

 an erect position, and is not improbably the upper part of one of 

 the species of Psaronius from the same locality. 



The second species, Caulojpteris antiqua, Newberry, is of much 

 larger size, but less perfectly preserved. It is a flattened stem on a 

 slab of marine limestone from the Corniferous formation in the lower 

 part of the Middle Devonian (Erian) of Ohio. 



The third species, Protopteris peregrina, Newberry, is from the 

 same formation with the last, and constitutes the first instance of 

 the occurrence of the genus to which it belongs, below the Carboni- 

 ferous. The specimens show the form and arrangement of the leaf- 

 scars, the microscopic structure of the petioles, and also the arrange- 

 ment of the aerial roots covering the lower part of the stem. 



The fourth species is a gigantic RJiachiopteris, or leaf-stalk, evi- 

 dently belonging to a species quite distinct from either of the above, 

 and showing its minute structure. It is no less than four inches 

 wide at the base. In the cellular tissue of this petiole are rounded 

 grains similar to those regarded by Corda and Carruthers, in Carbo- 

 niferous and Eocene specimens, as starch-granules. 



In addition to these species, the paper described a new Ncegge- 

 rathia (N. gilboensis), and noticed a remarkable specimen from 

 Caithness, in the collection of Prof. "Wyville Thomson, throwing 

 light on the problematical Lycopodites Vanuocemii of America ; 

 also interesting specimens of Psilophyton and other genera seen by 

 the writer in the collection of Mr. Peach of Edinburgh. 



XXVIII. Intelligence and Miscellaneous Articles. 



ON THE VELOCITY OE PROPAGATION OE ELECTItODYNAMIC ' 

 EEIECTS. BY DR. HELMHOLTZ. 



"]\/rANY investigators have recently been occupied with the question, 

 -^"-*- how are electrodynamic effects produced at a distance, — whether 

 (according to W. Weber) by forces of the moved electric particles 

 themselves operating immediately on the distant point, but which 

 depend on the velocities and accelerations of these particles in the 

 direction of the line joining them, or (according to C. Neumann, 

 jun.) by forces which diffuse themselves through space with a finite 

 velocity — or whether (according to Faraday and Maxwell) they are 

 occasioned only mediately, by a variation in the medium which fills 

 space. It is indeed a question of prime importance for the founda- 

 tions of physical science. -According to the two last-mentioned 

 views the distant electrodynamic effects of electric currents will not 

 be produced instantaneously, but the impulse to them will be propa- 

 gated through space with a finite velocity. In the theories of Neu- 

 mann and Maxwell this velocity is supposed, from electrodynamic 

 measurements, to be nearly equal to that of light. Nevertheless the 

 discussion lately published by me*, of electrodynamic theories, 

 showed that, according to what is accepted respecting the capability 

 * Journal fur reine unci avgew, Mathematik, vol. lxsii. Berlin. 



