July 24, 1914] 



SCIENCE 



135 



River Geratopsia to those of the Cow Island 

 beds is maxked. Lambe's Centrosaurus aper- 

 tus is mucb like Cope's Monoclonius crassus. 

 , Tbe skull of the great spiked dinosaur 8tyra- 

 cosaurus albertensis Lambe, the most unique 

 of the homed dinosaurs, appears to be related 

 to Cope's Monoclonius sphenocerus. The Ed- 

 monton Trachodon secured from Macheche 

 Creek six miles above DrumheUer, on the Eed 

 Deer Eiver, Alberta, is closely related to 

 Trachodon annectens from the Lance forma- 

 tion. Charles H. Sternberg 

 Geological Survey of Canada 



" hydraulics " in the encyclopedia britannica 

 To THE Editor op Science: While examin- 

 ing the article " Hydraulics " in the eleventh 

 edition of the Encyclopasdia Britannica, Vol. 

 14, p. 35, I discovered three errors, one of 

 which, at least, is worthy of note in Science, 

 as it may cause some one to lose valuable time 

 if the published figures are taken too seriously. 

 , The first and most serious of these errors is 

 the value of the coefficient of viscosity for 

 water at 77° F. which is stated to be 0.00000191 

 in lbs. i)er sq. ft. per unit velocity gradient in 

 feet per second.^ 



The correct equation for this value in C.G.S. 

 units is 



0.0178 

 Coefficient of viscosity = ^ _^ .03374+ .0002214= 



t being in centigrade degrees.^ 



If the numerator be multiplied by the num- 

 ber of square centimeters in one foot and 

 divided by the number of dynes in one 

 pound while the value of t is replaced by 

 it — 32) X 5 -^ 9, the expression for th© 

 coefficient of viscosity will become 



CJoefficient of viseoBlty^ 0.000 0372 



for water .4700 + .0144* -f .000068i» 



the units being the foot, pound and Fahrenheit 

 degree. 



If 77 be now substituted for t the result will 

 be the value of the coefficient for water at 

 77° F., or, 0.0000188, which is nearly ten times 

 the value given by the Encyclopaedia Bri- 

 tannica. 



1 See p. 35, upper right-hand part. 



2 See p. 536, Lamb's "Hydrodynamics," 1906. 



Another error occurs in the same article, 

 p. 77, near the top, equation (4). The last 

 sign in the right-hand member should be a 

 minus sign instead of a plus sign. The cor- 

 rect equation is 



H, = V ( 2iz,=fl-„ H- 5 + iS^) — iS,. (4) 



In Fig. 168, p. 90, the curve marked " Exper. 

 III." should be marked " Exper. I." and the 

 curve marked " Exper. I." should be marked 

 " Exper. m.," the numerals evidently being 

 transposed. 



The error in the coefficient of viscosity was 

 carried forward from the ninth edition of the 

 Encyclopaedia Britannica and was noted by 

 me in 1909 in a paper on backwater published 

 in The Minnesota Engineer, University of 

 Mumesota. B. F. Groat 



SCIENTIFIC BOOKS 

 Principles of Stratigraphy/. By Amadeus W. 

 Grabau, S.M., S.D., Professor of Paleontol- 

 ogy in Columbia University. New York, 

 A. G. Seller and Co. 1913. Pp. xxxii-f; 

 1185 + index, with numerous illustrations. 

 This is a monumental work, one which 

 presents fuUy and systematically the newer 

 viewpoints in the interpretation of the rocks 

 as the record of geologic history. For this 

 reason it will be of great value, especially to 

 the younger generation of American geologists, 

 in broadening their mental horizon and out- 

 lining the problems which rise for solution in 

 the twentieth century study of the rocks. It 

 differs from other manuals in the English 

 language to such a degree that it supplements 

 but does not supplant them. It contains a 

 notably large incorporation of material from 

 German sources and makes full use of recent 

 critical literature of both foreign and Ameri- 

 can authors. Nearly all of the older geologic 

 manuals, although valuable encyclopedias of 

 geologic science, have stored up the proven 

 knowledge of the past, but have not pointed 

 out the fields for investigation. They have 

 further emphasized facts and principles as 

 explaining facts, rather than as criteria of 

 interpretation. This work contains a wealth 

 of facts, though differing quite largely from 

 that assemblage which has been carried down 



