Reviews — The Linear Force of Growing Crystals. 223 



VII. — Note on the Linear Force oe Growing Crystals. By 

 George F. Becker and Arthur L. Day. Journal of Geology, 

 vol. xxiv, pp. 313-33, 1916. 



THE object of this paper is to re-affirm the thesis made by the 

 authors in 1905, viz. that the growth of crystals in saturated 

 solution develops a linear force in the direction of the load, and that 

 neither the magnitude of the load nor its character has any other 

 effect than to increase solubility, and so to raise the concentration 1 

 necessary for potential supersaturation and growth upon the loaded 

 crystals. The statement had been called into question by Bruhns 

 and Mecklenburg in 1913. The latter authors placed two crystals in 

 a similar saturated solution, the one loaded and the other free, and 

 remarked that the first did not lift its load. They entirely overlooked 

 that the solubility of the loaded crystal is for most substances greater 

 than that for the unloaded one, and further that the unloaded crystal 

 supports weight (its own). If the supersaturation of the liquid be 

 increased so that the free crystal cannot grow fast enough to keep the 

 concentration down, then the loaded crystal also will grow. 



VIII. — Crystals and Crystal Forces. By F. E. Wright. Journ. 

 Washington Acad. Sci., vol. vi, pp. 326-32, 1916. 



TN this short paper the author briefly rehearses what is known of 

 1. the structure of crystals and of interatomic forces, and considers 

 the methods by which further knowledge may be obtained. 

 Incidentally he mentions that at the Geophysical Laboratory at 

 Washington apparatus has been built or is under construction for 

 measuring accurately the changes in the crystallographical and 

 optical constants of crystals for temperatures ranging from — 190° 

 to -+- 1600° C, and for hydrostatic pressures ranging from 1 to 2000 

 atmospheres. He points out the striking fact in petrology, viz. the 

 fewness of the rock-making mineral species, especially in igneous 

 rocks, despite great diversity in conditions of formation and in 

 chemical composition. 



IX.— Fossil Fishes in the Collection of the United States 

 National Museum. By Charles R. Eastman. Proc. U.S. Nat. 

 Mus., vol. lii, pp. 235-304, pis. i-xxiii, 1917. 



THE fossil fish-remains in the U.S. National Museum at Washington 

 have lately been systematically arranged by Dr. Eastman, who 

 now publishes some notes on the collection, with figures and descrip- 

 tions of a few new species. Most interesting are the fragments from 

 old Palaeozoic formations, said to be of Ordovician age, in Colorado, 

 Montana, and South Dakota. One portion of a dermal plate, named 

 Astraspis desiderata, by Walcott, consists of tuberculated polygonal 

 tesserae, and is compared with the dorsomedian plate of Psatnmosteus 

 and Drepanaspis. It is unfortunate, however, that no new studies of 

 the microscopical structure of this and the associated fragments 

 appear to have been made. In the account of Devonian fish-remains 

 there are figures of a dorsomedian plate of Ceraspis carinata from the 



