1889.] Presents. 393 



mental way were constructed. In the more satisfactory form of the 

 apparatus an iron annulus surrounded by a coil of fine silk-covered 

 copper wire is embedded in a layer of paraffin wax between two glass 

 plates, and pieces of tinfoil are affixed on the outside surfaces of the 

 plates to serve as the coatings of a condenser. The electric displace- 

 ment passes through the aperture of the iron annulus. Any changes 

 in that displacement set up magnetic forces acting round the iron 

 annulus, which, thereby, is subjected to a varying magnetisation. The 

 annulus in turn sets up induction currents in the copper wire that 

 surrounds it, these induction currents being received and rendered 

 audible in an ordinary telephone receiver. The condenser is connected 

 to a Ruhmkorff coil which rapidly charges and discharges it. The 

 sounds heard in the telephone receiver establish the reality of the 

 magnetic action of the variations in the electric displacement. 



The author points out that this device, which may be regarded as 

 a new kind of proof plane for exploring varying electrostatic fields, is 

 probably capable of other useful applications, such as the investiga- 

 tion of specific inductive capacities. 



Presents, February 28, 1889. 

 Transactions. 



Baltimore : Johns Hopkins University. Studies (Historical and 

 Political Science). Vol. VI. 8vo. Baltimore 1888. 



The University. 



Brisbane : Royal Society of Queensland. Proceedings. Vol. V. 



Part 4. 8vo. Brisbane 1888. The Society. 



Cambridge, Mass. : Harvard College. Annual Reports. 1887-88. 



8vo. Cambridge 1889. The College. 



Dundee : University College. Museum of Zoology. Studies. 



Vol. I. Nos. 1-5, 4to. Dundee 1888-89. 



Professor D'Arcy Thompson. 



, London: Anthropological Institute. Journal. Vol. XVlII. No. 3. 



8vo. London 1889. The Institute. 



Geological Society. Quarterly Journal. Vol. XLV. No. 177. 



8vo. London 1889. The Society. 



Institution of Mechanical Engineers. Proceedings. 1888. No. 4. 



8vo. London. The Institution. 



Odontological Society of Great Britain. Transactions. Vol. 



XXI. No. 3. 8vo. London 1889. The Society. 



Royal Institution. Proceedings. Vol. XII. Part 2. 8vo. 



London 1889 ; List of Members, with Report of the Visitors, &c. 



1888. 8vo. London. The Institution. 



