July 26, 1901.] 



SCIENCE. 



145 



and other conditions rendering it relatively 

 somewhat inaccessible; and the quarter of a ter- 

 restrial meridian was finally adopted. It is 

 pleasing to note that throughout the discussion 

 which led to this result, the influential mem- 

 bers of the Commission, as well as many others 

 not members, stood out against the use of 

 any unit of length or mass already iu use in 

 France, as it was recognized that such use 

 would be an obstacle to the introduction of the 

 system among the people of other nations. An 

 interesting episode of the initiative of the arc 

 measurement was a controversy over the use of 

 a sector in the determination of latitude or the 

 newly invented repeating circle of Borda. 

 Indeed it seems not unlikely that ' a desire to 

 make the reputation of the circle of Borda ' had 

 some influence in the choice of the new stand- 

 ard as against the seconds pendulum. De- 

 lambre proposed to Borda to employ both sector 

 and circle, but the latter dryly intimated that 

 it was desired to ascertain if the sectors were 

 good, and the matter was not pressed. 



When the Commission was received by the 

 King, Louis XVI., after its recommendations 

 had been approved and before the formal be- 

 ginning of its operations, his majesty, speaking 

 to each one in turn of the special duties that 

 had been assigned to him, asked Cassini (the 

 fourth eminent astronomer bearing that name), 

 to whom had been assigned the triangulation 

 and measurement of latitudes, how it was that 

 he was going to remeasure an arc of the 

 meridian that his father and grandfather had 

 already done before him. Did he hope to do 

 better- than they? To which Cassini replied 

 that he would not so flatter himself, if he had 

 not a great advantage over them in the fact 

 that while the instruments which they used in 

 measuring angles gave results correct to within 

 fifteen seconds, that invented by Borda would 

 enable him to reach a precision of one second. 



M. Bigourdan's volume contains much de- 

 tailed information relating to the work of the 

 Commissions, with many interesting and impor- 

 tant citations from original documents. The 

 fundamental legislation by which the system 

 was founded is fully discussed, the opposition 

 to it is fairly presented, and the subsequent 

 legislation and discussion leading to its final 



adoption by the nation as a whole receive sat- 

 isfactory treatment. There is a chapter on the 

 propagation of the system among foreign 

 nations which leads up to the appointment of 

 an international metric commission about 1870, 

 and to the establishment of the International 

 Bureau of Weights and Measures about 1875. 

 The splendid work of the latter during the 

 twenty-five years of its activity is treated in 

 soEpe detail and forms a fitting close to a most 

 useful and interesting contribution to the his- 

 tory of metrology. 



T. C. Mendenhall. p, 



A Treatise on Electromagnetic Phenomena and on r- 

 the Compass and its Deviations Aboard Ship, 

 Mathematical, Theoretical and Practical. By 

 Commander T. A. Lyons, U. S. Navy. John 

 Wiley & Sons. 



The first volume of this treatise, the only one 

 yet published, deals with electromagnetic phe- 

 nomena, or radiation in all its protean forms. 

 If the reader wants information about sun-spots 

 or aurorse, about Crookes's fourth state of mat- 

 ter or Bjerknes's imitations of magnetic fields 

 by pulsating discs, about the work of Hertz or 

 the genesis and action of Rontgen rays, he will 

 find it in this introductory volume. However 

 many and however diverse the subjects dis- 

 cussed, they are all treated from the point of 

 view of the wave-theory. Commander Lyons 

 seems to hold a brief for the ether whose exis- 

 tence he seeks to remove from the condition of 

 a working hypothesis and whose properties he 

 tries very hard to define. This is indeed a dif- 

 ficult task ; for he tells us, on page 9, that " the 

 mathematician attributes to the ether properties 

 necessary to the formation of equations express- 

 ing its energy ; the physicist ascribes to it 

 qualities essential to the explanation of facts : 

 the electrician meets conditions that require 

 further hypotheses ; still others do not accept 

 fully any one of these conceptions ; and some 

 even reject the ether altogether." 



So conscious is the author of the paramount 

 importance in physics and philosophical specu- 

 lation of the medium which fills intermolecular 

 as well as interstellar space, that he dwells with 

 great insistence upon the experimental evidence 

 which there is for its existence. He is so eager 



