the most curious forms of the experiment is the one shown in Fig. 2.  Here a third person, C, hears the hands of A and B speak when a circuit is formed by means of three persons, A, B, and C, the two former, A and B, each holding one of the wires of the circuit and applying his free hand to the ear of C. Although the experiment is one that requires entire silence, and could not on that account be performed at the laboratory, a sort of telephonic chain can be formed in which five or six persons may hear at the same time.  A, putting his hand on the ear of B, the latter putting his to that of C, and so on up to the last person, who closes the circuit by grasping one of the handles, the other one being held by A.

[Illustration:  EXPERIMENT ON TELEPHONIC TRANSMISSION WITHOUT RECEIVING APPARATUS.]

It is difficult in the present state of science to explain very clearly how these telephonic transmissions are effected without a receiver.  All that we can conclude from it so far is that the ear is an instrument of incomparable delicacy and of exquisite sensitiveness, since it perceives vibrations in which the energy developer, particularly in the telephonic chain, is exceedingly feeble.

Without any desire to seek an application for an experiment that is simply curious, we yet believe that there is here a phenomenon of a nature to be studied by physicists.  Discoveries in telephony and microphony have certainly opened up to science, as regards both theory and practice, new horizons that still promise other surprises for the future.  But to return to the observatory:  The success obtained by the exhibition of the French Society of Physics shows that these reunions respond to a genuine need—­that of instructing in and popularizing science.  While warmly congratulating the organizers of these meetings, we may express a wish that the good example set by the Society of Physics may be followed by other societies.  We are convinced in advance that an equal success awaits them.—­La Nature.

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ON THE ARRANGEMENT OF GROUND CONDUCTORS.

In telegraphy, as well as in the question of lightning rods, attention has been but incidentally paid to the improvement of ground conductors, and this point has not been the object of that careful study that has been bestowed upon the establishment of aerial lines.  It is only recently that the interest created by lightning rods has given rise to new forms of conductors differing from those formerly used.  The publications of the Prussian Academy of Sciences of from 1876 to 1880 contain some information of special importance in regard to this.  It is stated therein that the effect of ground conductors may be notably increased by the division of the earth plates and the use of metallic rods, without necessitating a greater output of material.  These facts, however, have not as yet been put to profit in practice for the