September 11, 1896.] 



SCIENCE. 



349 



point the vergency of tlie beam. Assuming 

 the luminous source to be of uniforra bright- 

 ness, he shows that the quotient— intensity 

 of beam divided by vergency — is a constant; 

 this he calls the compactness of the beam. 

 He applies this conception to the discussion 

 of various theorems in connection with 

 optical instruments. 

 Some Points in the Mechanical Conception of 



the Electro-magnetic Field : By W. S. 



Franklin". 



The author pointed out the importance of 

 applying the conceptions of Maxwell and 

 Lodge directly to the explanation of funda- 

 mental principles instead of to special 

 cases. In addition to the explanation of 

 the two laws of induction he applied the 

 conceptions of Maxwell to the explanation 

 of the energy stream and to the explana- 

 tion of electro-magnetic waves. 

 Mechanical Models of the Circuit : By Bkown 



Atres. 



The author exhibited a model consisting 

 of a number of fly-wheels arranged in a 

 circuit with spring connections. The 

 model represented in a striking manner 

 nearly all of the fundamental phenomena 

 of the electric circuit, particularly the 

 phenomena of electrical oscillation and res- 

 onance. 

 Graphical Treatment of Alternating Currents in 



Branching Circuits : By Henry T. Eddy. 



The author gave an elegant treatment of 

 the general problem of branched circuits 

 containing resistance, inductance and capac- 

 ity, showing the construction of the locus 

 of the resultant current vector for varying 

 frequency. 

 Description and Exhibition of a Convenient Form 



of the ' Interferential Comparer,'' and of an 



Interferential Caliper Attachment for Use in 



Physical Laboratories : By W. A. Bogers. 



Description and Exhibition of a Bench Compar- 

 ator for General Use in Physical Laboratories : 

 By W. A. EoGERS. 



On the Ride for the Dynamo and Motor : By 



Alexander Macparlane. 



In the discussion of this paper Prof. S. T. 

 Moreland gave a mnemonic rule, not gen- 

 erally known, associating the directions of 

 the electric current and of the magnetic 

 field with the hand in such a way that the 

 force is in the direction one would natu- 

 rally push. 



Note on the Effect of Odd Harmonics upon the 

 Virtual Values of periodically varying Quan- 

 tities : By Frederick: Bedell and James 

 E. Boyd. 



The authors showed that the virtual value 

 of a periodic E. M. F. is independent of the 

 phase relations of its odd harmonics, but de- 

 pendent only upon their amplitudes. 

 Experimental Determination of the Relative 

 Amounts of Worh Done in changing the 

 Lengths of two metal Bars under the same 

 Thermal Conditions, by an Envelope of Heated 

 Air, and by Pure Radiations in a Vacuum : 

 By W. A. EoGERs. 



The author explained the difference in the 

 behavior of a metal bar in an air bath and 

 in a vacuum. 



An Experimental Method of Finding the Value 

 of a Unit of Force in A'^y System Whatever : 

 By W. A. Rogers. 

 A new Alternating Current Curve-tracer : By 

 Edward B. Eosa. 



The author described an apparatus by 

 means of which the successive points in an 

 alternate current or E. M. F. curve are 

 platted directly, avoiding the necessity of 

 taking and entering numerical observations. 

 He exhibited a large number of curves, 

 originals and enlargements. 

 Visible Electric Waves: By B. E. Moore. 



The author described an arrangement in 

 which stationary electric waves on a wire 

 are rendered visible by the brush discharge 

 from the various portions of the wire. 

 Electrical Waves in Long Parallel Wires : By 

 A. D. Cole. 



