908 



SCIENCE 



[N. S. Vol. XLII. No. 1095 



cepts." It fits exactly the poundals, slugs, gee- 

 pounds, engineers' unit of mass, gravitals, 

 micro-speedals, kinetic unit, scientific unit, 

 absolute and gravitational systems, " concepts 

 of mass," " force is the space rate at which 

 work in foot pounds is done, it is also the time 

 rate at which momentum is produced or de- 

 stroyed " (Perry's " Calculus ") and all such 

 pedagogical rubbish. 



Our first object is to get the student into a posi- 

 tion where he can solve such simple problems as 

 he sees in actual work about him, and a certain 

 amount of ignorance which would be very lament- 

 able on the part of myself and your other contrib- 

 utors, is highly praiseworthy in the student. 



Good! E"ow will Professor Wilson examine 

 the simple problem I have given and my 

 method of solving it and get one of his in- 

 structors to experiment on the method with 

 some freshmen students and report the result? 

 " Try it on the dog." Test it not only by the 

 canons of logic and of common sense, but also 

 by experience. 



Any student knows what a weight of four 

 pounds is. 



Of course he does, until he begins the study 

 of physics; then he may be in some doubt 

 about it. He knows that it is a piece of metal 

 with " 4 lb." stamped on it, but when he is 

 told that that is not a weight, but mass, and 

 that a weight of four pounds means a force of 

 four pounds, also that a mass is " the constant 

 ratio of force to acceleration," and that " he 

 can not acquire the desired ideas of mass and 

 inertia until after the ideas of force and 

 acceleration have been accepted," it is no 

 wonder that he becomes confused, and replies 

 to the simple question, "What is force?" 

 " The time-rate of the change of momentimi,'' 

 quoting from the text-book, without knowing 

 what the words mean. 



Wii. Kent 



A MNEMONIC COUPLET FOR GEOLOGIC PERIODS 



Several years of experience in teaching 

 geology led me, some time since, to the inven- 

 tion or discovery of the following scheme for 

 helping students to remember the order of 

 geologic periods. 



The fonn offered here is adapted to the plan 

 presented in Chamberlin and Salisbury's " Col- 

 lege Geology," which is widely used. It may 

 be modified without serious difficulty to suit 

 other time divisions. 



Neglecting the Pre-Cambrian, somewhat as 

 common histories do pre-historic time, and also 

 the recent epoch, we take the periods of the 

 Paleozoic era, Cambrian, Ordovician, Silurian, 

 Devonian, Mississippian, Pennsylvanian and 

 Permian; of the Mesozoic, Triassie, Jurassic, 

 Comanche and Cretaceous; and of the Ceno- 

 zoic. Eocene (Oligocene), Miocene, Pliocene 

 and Pleistocene. 



Taking the first syllable of each period, and 

 adding the termination ice to the Permian to 

 commemorate the glacial epoch of that time, 

 and also to rhyme with " Pleis," which also re- 

 minds one of the better known epoch of the 

 same sort, we have the following jingle: 



Cam.Or.Sil.De. 



Miss.Penn.Perm-ice, 

 Tri.Ju.Co.Cre. 



E.(01.).Mi.Pli.Pleis. 



Some of the divisions here counted periods 

 may be more fittingly called epochs, but that 

 makes no difference with the order. 



J. E. Todd 



Univeesitt op Kansas 



VARIATION IN CENOTHERA HEWETTI 



Dr. G. H. Shull^ recently published a paper 

 on " A Peculiar Negative Correlation in 

 (Enothera Hybrids," in which he showed that 

 in certain cultures dull dark red stems were 

 associated with entirely green buds, and gave 

 other evidence indicating that the appearance 

 of anthocyan in one part of the plant by no 

 means involved its appearance in other parts. 



I have this year a series of plants of GEno- 

 thera hewetti, descended from the original 

 plant brought from the Rito de los Frijoles, 

 New Mexico, in 1912. This is a relative of (E. 

 hooheri, and quite distinct from the species 

 used by Dr. Shull. Nevertheless, it varies in 

 pigmentation along practically the same lines. 



1- Journal of Genetics, IV., 1914, p. 83. 



