296 



SCIENCE 



[Vol. IV., No. 85. 



handwriting and computations of this intellectual 

 giant, whose works will for all time be the greatest 

 wonder to him who studies them the most. 



With the hearty thanks of the section to Professor 

 Adams for his exceedingly interesting communica- 

 tions, it was then adjourned. 



PROCEEDINGS OF THE SECTION OF 

 PHYSICS. 



The meeting of the American association was one 

 of unusual interest and importance to the members 

 of section B. This is to be attributed not only to the 

 unusually large attendance of American physicists, 

 but also to the presence of a number of distinguished 

 members of the British association, who have con- 

 tributed to the success of the meetings not only by 

 presenting papers, but by entering freely into the dis- 

 cussions. In particular the section was fortunate in 

 having the presence of Sir William Thomson, to whom 

 more than to any one else we owe the successful op- 

 eration of the great ocean cables, and who stands with 

 Helmholtz first among living physicists. Whenever 

 he entered any of the discussions, all were benefited 

 by the clearness and suggestiveness of his remarks. 



Among the members of the British association who 

 were present, may also be mentioned Professor Fitz- 

 gerald of the University of Dublin, Professor Silvanus , 

 P. Thompson, Mr. W. EL Preece, superintendent of 

 the English postal telegraph, Professor Forbes, and 

 Professor Schuster of the Cavendish laboratory. 



Among American physicists there were Professors 

 Trowbridge, Rowland, Barker, Mendenhall, Hall, 

 Hastings, Bell, Anthony, Brackett, Rogers, Picker- 

 ing, Cross, and many others. The section was organ- 

 ized on Thursday, Sept. 4, and the opening address 

 delivered by the vice-president, Professor Trowbridge. 

 The time devoted to the reading and discussion of 

 papers was unfortunately much infringed upon by the 

 Electrical conference: yet, considering this serious 

 interruption, the number of interesting discussions 

 was unusually large. 



It is not to be expected that the elaborate investiga- 

 tion of the relation of the yard to the metre, such as 

 was the subject of a paper by Professor William A. 

 Rogers, will be of very general interest. Yet to the 

 physicist such a comparison, conducted by one who 

 has had the long experience of Professor Rogers, is of 

 the highest importance in giving accuracy to determi- 

 nations of length. Professor Rogers has given his life 

 to perfecting the construction and testing of standards 

 of length, and the result of this his latest investiga- 

 tion is that the metre is 39.37027 inches in length. 

 One of the most important physical measurements is 

 that of the wave-length of light of any given degree of 

 refrangibility, and this determination is best made by 

 means of the diffraction grating. On account of the 

 extensive use of the magnificent gratings constructed 

 by Professor Rowland for this purpose, Professor 

 Rogers instituted an investigation to determine the 

 coefficient of expansion of the speculum-metal used 



in the construction of these gratings. He also noted 

 that from its homogeneity, fineness of grain, and non- 

 liability to tarnish, this speculum-metal is peculiarly 

 suitable for constructing fine scales, though its ex- 

 treme brittleness is an objection to its use for large 

 scales. Professor Rowland stated that he proposed to 

 construct scales on his ruling-engine which would en- 

 able the physicist at any time, by purely optical means, 

 and without knowing the coefficient of expansion 

 of the metal or its temperature, to obtain the value of 

 the length of the scale in terms of the wave-length 

 of any given ray of light. These scales were simply to 

 be straight pieces of speculum-metal ruled with lines 

 just as an ordinary grating, except that the length of 

 the lines is to be only about one centimetre, every 

 one-hundredth line being somewhat longer than its 

 neighbors: the whole ruled strip is to be one deci- 

 metre in length. From the manner of ruling, it will 

 be easy to count the whole number of lines in the 

 length of the strip, and then by a simple use of the 

 scale as a grating in a suitable spectrometer the whole 

 length may be immediately found at any time in terms 

 of any specified wave-length of light. 



In some forms of telephones and in the microphone, 

 the action depends on the change in resistance of a 

 small carbon button on being subjected to pressure. 

 There has been much discussion as to whether this 

 diminution of the resistance with pressure is due to a 

 change in the resistance of the carbon itself, or simply 

 to the better contact made between the carbon and 

 the metallic conductor when the pressure is applied. 

 Professor Mendenhall has carried out some experi- 

 ments to determine the question; and one of his 

 methods of experimenting — that with the hard car- 

 bons — appears to point conclusively in favor of the 

 theory that the resistance of the carbon itself is 

 altered by pressure. The experiments made by him 

 on soft carbon are open to criticism, though they also 

 point to the change taking place in the carbon. Pro- 

 fessor Mendenhall finds that the resistance is not 

 simply proportional to the pressure, and thinks that 

 by increasing the pressure a point of maximum con- 

 ductivity would be reached where there would be no 

 change in resistance for a small change in pressure. 



Prof. A. Graham Bell, the inventor of the tele- 

 phone, read a paper giving a possible method of 

 communication between ships at sea. The simple 

 experiment that illustrates the method which he 

 proposed is as follows : Take a basin of water, intro- 

 duce into it, at two widely separated points, the two 

 terminals of a battery-circuit which contains an in- 

 terrupter, making and breaking the circuit very rap- 

 idly. Now at two other points touch the water with 

 the terminals of a circuit containing a telephone. 

 A sound will be heard, except when the two tele- 

 phone terminals touch the water at points where the 

 potential is the same. In this way the equipotential 

 lines can easily be picked out. Now, to apply this 

 to the case of a ship at sea: Suppose one ship to be 

 provided with a dynamo-machine generating a pow- 

 erful current, and let one terminal enter the water 

 at the prow of the ship, and the other be carefully 

 insulated, except at its end, and be trailed behind 



