514 



SCIENCE. 



[N. S. Vol. III. No. 66. 



open to dispute and, with their brethren the 

 mathematicians, generally prefer to begin a 

 discussion by defining the terms they are about 

 to use, unless such terms are already so re- 

 stricted and definite in their meaning as to cause 

 no doubt. 



Failure to pursue this course is the basis of 

 much idle talk and meaningless controversy, 

 especially at the present time. 



People are everywhere talking about an 

 'honest dollar,' or 'sound money,' without 

 stopping to ask what a dollar is, or what is 

 meant by 'money,' or a 'standard of value,' 

 without inquiring what is ' a standard and 

 what is meant by value,' and all of this to the 

 confusion of many who would like to give 

 serious thought to important subjects. As 

 Major Powell's philosophy is to furnish a basis 

 for the elementary concepts of physical science, 

 he will not, I am sure, take it amiss if he is 

 asked in the beginning to define with some care 

 the principal terms of which he makes use. No 

 physicist can fail to read his last paper with 

 much interest and, it may be added, with no 

 little astonishment. To one accustomed to the 

 rather simple perspective of the so-called exact 

 sciences, there is a sort of mistiness and ob- 

 scurity in it which suggests an ' impressionist's ' 

 view of the subject. 



It is true that in the beginning definitions of 

 'body,' 'particle,' 'molecule,' 'atom,' etc., are 

 given, which are quite satisfactory as represent- 

 ing the meaning which the author proposes to 

 attach to these words. But the physicists are 

 put entirely out of the controversy by the 

 failure of the author to tell or even hint at 

 what he means by that which is the text of the 

 whole paper, namely, motion itself. Major 

 Powell undertakes to show that ' 'motion is per- 

 sistent," that it "cannot be created or annihila- 

 ted," and he even goes so far as to declare that 

 this has been demonstrated to the satisfaction 

 of a great body of scientific men. He speaks, 

 often, of 'motion as speed,' thus creating an 

 anxiety to know what ' motion ' is when it is not 

 ' speed. ' By ' speed ' he evidently means ' ve- 

 locity ' as independent of direction, and he de- 

 clares that ' motion as speed ' is ' inherent in 

 matter ' and is not imposed upon it from with- 

 out, from which it necessarilv follows that it can- 



not be transferred from one system to another. 

 Acceleration, he then says, must be considered 

 as ' deflection ' or change in that element of 

 motion which is ' direction,' and not in any cor- 

 rect sense a change in velocity. No one will 

 deny a considerable ingenuity in reaching this^ 

 conclusion, but there are a few obstacles in the 

 way which Major Powell will doubtless easily 

 sweep aside, some of them being suggested in 

 the following questions : 



1. What is motion ? 



2. What is rest ? 



3. If by ' motion as speed ' is meant ' velocitj'^, ' 

 and if by its ' persistence ' is meant invaria- 

 bility of velocity, what possesses this invaria- 

 bility? — ^bodies, molecules, particles, atoms? — - 

 and in reference to what is the velocity constant ? 



4. As a molecule is considered as a ' body ' 

 when reference is had to the atoms which com- 

 pose it. can it have an ' invariable velocity ' as 

 a molecule and variable velocity as a ' body '? 



Many other doubts suggest themselves which 

 will probably be quieted by the answers to 

 these questions. I cannot refrain from express- 

 ing a hope, however, that in addition to these 

 answers. Major Powell will kindly furnish an 

 explanation of what he means when he says 

 that the transmission of light at the rate of 

 299,878,000 metres per second furnishes an ex- 

 ample of ' particle motion at a velocity so 

 great that any observed molecular motion sinks 

 into insignificance. ' M. 



Mabch 23, 1896. 



principles of maeine zoogeogeaphy. 



I HAVE been much interested in the admi- 

 rable review, by Dr. Baur,* of Dr. Ortmann's 

 ' Grundziige der marinen Tiergeographie, ' which 

 I had only previously known from the ' sum- 

 mary ' given in ' the Princeton College Bulletin ' 

 (VII., pp. 100-107); since then I have had the 

 pleasure of receiving the work itself from the 

 learned author. I find similarity in some 

 features and difference in others between the 

 views of Dr. Ortmann and my own. My con- 

 tributions to zoogeography appears to have 

 been unknown to Dr. Ortmann, except at sec- 

 ond-hand, although exact references were made 

 to publications by Dr. Faxon (p. 233), through 



* Science, N. S., III., 359-367, March 6, 1896. 



