362 ABSTRACTS OF SCIENTIFIC PAPERS 



XXV. Note on the Electrification of an Island. ' Nature,' May 5, 

 1870, vol. ii. p. 12 ; ' American Journal of Science,' 1870. 



This note describes a curious observation made by Mr. Gott, the 

 superintendent of the French Cable Company's station on the Island 

 of St. Pierre Miquelon, that the Morse signals sent from another 

 station on the island could be read on the Siphon Recorder of the 

 French Company, when that instrument was placed between an 

 earth plate at the station and another earth three miles out at sea. 

 A sample of recorder slip with a Morse message stolen in this way 

 is reproduced in the paper. The author explains the result by de- 

 scribing the potential of the ground in the neighbourhood of both 

 stations as alternately raised and lowered by the battery used to 

 send Morse signals, so that the island discharged itself through the 

 short insulated line which connected the French Company's station 

 with their distant sea ' earth.' He adds that the action could be 

 avoided by the exclusive use of sea ' earths,' according to the plan 

 introduced by Mr. C. F. Varley to eliminate natural earth-currents. 



XXVI. On the Practical Application of Reciprocal Figures to the 

 Calculation of Strains on Framework. ' Transactions of the 

 Royal Society of Edinburgh,' 1869, vol. xxv. p. 441. 



The scope of this paper is best shown by quoting the introductory 

 paragraphs : 



' The theory of reciprocal figures used as diagrams of forces was 

 first completely stated by Professor J. Clerk Maxwell, in a paper 

 published in the "Philosophical Magazine," April 1864. The follow- 

 ing definition of reciprocal plane figures, and their application to 

 statics, are there given as follows : 



' " Two plane figures are reciprocal when they consist of an equal 

 number of lines, so that corresponding lines in the two figures are 

 parallel, and corresponding lines which converge to a point in one 

 figure form a closed polygon in the other." 



' " If forces represented in magnitude by two lines of a figure be 

 made to act between the extremities of the corresponding lines of 

 the reciprocal figure, then the points of the reciprocal figure will all 

 be in equilibrium under the action of these forces." 



' The demonstration of this statement is given. The conditions 

 under which stresses are determinate, and some examples of reci- 

 procal figures, are also given in the paper, which leaves nothing to 

 be desired by the mathematician. 



' Few engineers would, however, suspect that the two paragraphs 



