Jan. 



30. 1879] 



NATURE 



297 



over the groove made in the soft-iron bars is still less 

 extensible ; and finally, when the thread has taken the 

 ciu-vature of the surrounding parts, it opposes any further 

 descent of the armature with the resistance which a 

 stretched thread of india-rubber presents against being 

 pressed or crushed. 



This apparatus, to which M. Marey has given the name 

 electrodynarnograph, has still to receive further improve- 

 ments, but even as it is, it has already furnished some 

 interesting evidence as to the decrease in volume of the 

 electric waves from the beginning to the end of the dis- 



charge ; also as to the shape of these waves and the 

 occurrence in the electric tetanus produced by strych- 

 nine, &c. (_ f these different results we shall at present 

 consider only one — the form of a wave is traced by the 

 electro-dynamograph : — an investigation which brings us 

 to the analysis of the wave-phases. 



In Fig. 6 the continuous line b is the tracing of a 

 single wave obtained with the electro-dynamograph. 

 From it alone we already have evidence that the ascend- 

 ing phase is much more sudden than the descending 

 phase as also takes place in a muscular shock. We can 



Fig. 4- 



further theoretically complete the cune by taking into 

 account what we have learned by Guillemin's method in 

 the preceding paragraph about the duration of a wave. 

 All that is necessary is to produce downwards the two 

 ascending and descending lines till they intercept be- 

 tween them a distance equal to that which represents 

 (on the time-line) the duration of the whole wave. Thus 

 (Fig. 6) the pointed line a represents the actual position 

 of the axis of abscissas and that part of the tracing which 

 the instrument was unable to trace on account of its 

 insufficient sensibility. 



It is true that this curve is only probable, but there 



F1&6. 



are great presumptions in favour of its reality. The 

 points of origin and termination can determine it expe- 

 rimentally, as we have seen done by Guillemin's method 

 (see 2). 



We can now understand the reason of the special cha- 

 racteristics presented by currents induced in a secondary 

 coil by the waves of a torpedo discharge which have 

 been passed through an inducting coil. The phase of 

 sudden increase of each wave is alone capable of giving 

 birth to an inducted current. FRANCOIS Franck 



{To be continued.) 



GEOGRAPHICAL NOTES 



At the meeting of the Geographical Society on Monday, 

 Sir H. Rawlinson read a paper. On the road to Merv^from 

 the Caspian. After some interesting remarks on the 

 comparative geography of the eastern shores of the Caspian 

 Sea, Sir Henry read some portion of the Russian letters 

 on the earlier stages of the road to Merv, of which a 

 summary appeared in our last issue, and afterivards gave 

 from Russian official documents an account of two 

 ancient cities, the probable relics of Khowrasmian times— 

 Mestorian, or Mestdovran, and Meshed. The former 

 in past ages was one of the most important cities of 

 Central Asia, if one may judge from the remarkable 

 aqueducts leading into it, which were the chief 

 arteries of an entire system of irrigation canals tho- 

 roughly watering the whole countrj', and from the 

 number of its buildings, the remains of which exist to 

 this day. The course of the aqueduct was explored by 

 General Lomakine's orders some two or three years ago, 

 and was traced to the Sumbar, a tributary of the Attrek, 

 a length of some sixty-five versts. The city of Mestorian 

 appears to have consisted of a citadel and of two other 

 mclosures with thick, high walls built of enormous bricks. 

 The mass of [the debris at the place is so extensive and 

 in such good preservation, that it would be possible, we 



are told, to make use of it for building a large new town ! 

 The bricks, it may be added, are stated to be as hard as 

 stone, and often carved and ornamented with friezes in 

 relief, arabesques, and well-executed inscriptions ; the 

 last are sometimes in various colours, illuminated with 

 flowers, and the letters about seven inches in height. 

 Five versts from Mestorian is another remarkable place, 

 known in the country as Meshed ; it is, strictly speak- 

 ing, an ancient necropolis. Here, according to report, 

 is an open coffer holding the sacred books, a hanging 

 lamp, and vases for ablutions, and although in a desert 

 place and wholly unprotected, no one dreams of touching 

 its contents. Sir Henry Rawlinson afterwards dealt at 

 some length with the geography of the country further to 

 the eastward, more especially with that on the northern 

 slopes of the Attock, which is inhabited by three divisions 

 of the Tekkd Turcoman tribes. 



We regret to record the death, on Saturday afternoon, 

 at a comparatively early age, of Commander G. C. 

 Musters, so well known as the explorer of Patagonia. His 

 work, "At Home with the Patagonians," is at present the 

 best authority we have on this inhospitable country and 

 its people, and Mr. Musters, as readers of the work know, 

 obtained his information by living with the Patagonians 

 for many months as their " king," and it w^as only by a 

 ruse that he managed to get away from a people who 



