June 26, 1914] 



SCIENCE 



927 



Professor and Mrs. H. M. Hall have given 

 us of the Tosemite. 



We have had a feeling that our manuals 

 must cover vast sections of the country, 

 many hundreds of thousands of square 

 miles; that they must be complete, ac- 

 counting for everything ever mentioned. 

 As a result much is found in our volumes 

 that describes things that do not exist, are 

 very rare or have only historical interest 

 for the technically trained. I am pleading 

 for those who want to know the plants that 

 relate themselves to their professional 

 work, to their mental life or to their recrea- 

 tions. Please note I said know the plants, 

 not know plant names. No one wishes to 

 know names apart from the plants in which 

 he is interested. Knowing the plant is first, 

 and then a name becomes indispensable. 



And why not a name instead of a manu- 

 factured phrase palmed off as an English 

 name ? In what respect is ' ' purple-stemmed 

 swamp beggar ticks ' ' better than the name ? 

 We use geranium, magnolia, forsythia, and 

 scores of others. Why not phlox, merten- 

 sia, chrysopsis or practically any other 

 generic name? It is true this only desig- 

 nates the genus, but this is all that many 

 who are intensely interested in the plants 

 care to know, as exemplified by our use 

 of the words clematis, chrysanthemum, 

 lupines and roses. Those who wish to 

 designate the species can do so with more 

 celerity and certainty by saying Phlox 

 glabrata than by smooth-leaved sweet 

 William. In my recent "Spring Flora" 

 I proposed this use of the generic name 

 seriously and I wish to assert that I have 

 seen no reason for changing my opinion. 



In closing let me express the belief that 

 we are on the eve of a new era. Already 

 the pendulum is swinging back. The dis- 

 memberment of genera and the multiplica- 

 tions of species proceed more cautiously. 

 New species will continue to be found even 



in this country (hundreds of them). These 

 ought to be and will be published. So long 

 as work is done errors must occur, but the 

 percentage of error, let us hope, will be 

 greatly reduced, while the disturbing effect 

 will be minimized by more and more of 

 constructive work of the compendium type. 



AvEN Nelson 

 University of Wyoming, 

 Laeamib, Wyo. 



ON AN EXPEBIMENTAL DETEBMINATION 



OF THE EARTH'S ELASTIC 



PEOFERTIES 



It is well known that the ocean tides are 

 caused by the differences in the attraction of 

 the sun and moon for the surface and center 

 of the earth. These differential forces are 

 very small compared with the attraction of the 

 earth for bodies on its surface; in round num- 

 bers the joint tidal force of the sun and moon 

 on a body at the earth's surface under the 

 most favorable circumstances amounts to only 

 about 1/10,000,000 of the weight of the body. 

 This force woiild deflect the bob of a plumb 

 line 10 feet long from its normal position only 

 about 1/100,000 of an inch. This deviation 

 corresponds to an angle of only .02", or the 

 angle which the head of a pin would subtend 

 at a distance of 10 miles. 



If the earth were a perfectly fluid mass, i. e., 

 if it offered no resistance, either elastic or 

 viscous, to changes of shape, the surface would 

 be tilted by the tidal forces through this same 

 angle, and the new horizontal would be per- 

 pendicular to the new vertical. There would 

 therefore be no change of the plumb-line rela- 

 tive to the earth's surface, and we could not 

 detect the so-called " deflection of the vertical." 



If the earth were perfectly rigid the plumb 

 line would move back and forth, as the posi- 

 tions of the sun and moon vary, by an amount 

 which can be calculated with an accuracy 

 which is limited only by our knowledge of the 

 masses and relative positions of the sun, earth 

 and moon. As a matter of fact, the earth is 

 partially and not entirely rigid, and therefore 

 the excursions of the plumb line are a certain 



