Feb. 3. 1887 J 



NA rURE 



ij^ones describe bends and sinuosities of a most peculiar 

 character. As Dr. Naumann states, these results seem to open 

 up a nesv field of research quite worth investigating. 



.V PAPER of unusual scientific interest was read at Monday's 

 111' cling of the Royal Geographical Society by Mr. II. J. 

 M.iokiiider, I5..\. (O.tford), on the field and methods of geo- 

 graphy. Mr. Mackinder aimed at showing how geograjshy could 

 be made more than a mere cultivation of dry facts, and become 

 indeed a department of scientific inquiry. He takes man as the 

 centre of the field and defines geography as the study of man in 

 relation to so much of his environment as varies locally ; Mr. 

 Mackinder thus takes geoijraphy to be the physical basis of 

 history. He insists on a clear separation being m.ade between 

 physical geography and both geology and physiography. The 

 physical geographer has 10 deal with only so much of the past as 

 will enable him to interpret the present, whereas the geologist deals 

 with the present, only that he may be able to Interpret the past. 

 So with other departments of .science, as meteorology ; from the 

 new stand-point only so much of them is to be included as is 

 pertinent to the geographical line of investigation. Mr. Mac- 

 kinder illustrated his position by two sets of three maps — one of 

 South-Easlern England, physical, geological, political ; and the 

 other of India, showing physical features in relation to rainfall 

 and population. lie attempted to show, on the basis of physical 

 conditions, why, among other things, London should have 

 become the metropolis of the Empire and why the three south- 

 eastern counties should have h.id their existing boundaries. 

 With reference to India, again, he showed how geographical 

 conditions determined that Delhi and Calcutta should have 

 become the ancient and modern capitals of India. Geography, 

 when studied in this way, Mr. M.ackinder thinks, might become 

 a bridge between the physical sciences on the one hand and 

 classical and historical studies on the other. The lecture was 

 illustrated by some very fine and instructive maps and lantern 

 views. 



PHYSICAL NOTES 



The inverse electromotive force of the voltaic arc has recently 

 been investigated by Prof. C. R. Cross, of the Massachusetts 

 Institute of Technology, and by Mr. W. h". .Shepard. It ap- 

 pears that with currents varying from 3 to 10 amperes the inverse 

 electromotive force is about 39 volts when the arc is silent, 

 and about 15 volts when it is hissing ; but both these values 

 show a diminution as the currents employed are increased. The 

 transition from one state to the other is abrupt. Addition of 

 volatile metallic salts to the arc always decreases the inverse 

 electromotive force. In rarefied air the inverse electro- 

 motive force is unaltered, but the true re istance of the arc is 

 diminished. 



Sensitive hygrometers have lately been constructed upon 

 ^ principle resembling liregnet's metallic thermometer. A spiral 

 iiposed of two substances having different hygrometric co- 

 ioients of expansion tends to curl or uncurl according to 

 . ii.mges in the hygrometric state of the air. Some of these have 

 licen made by Prof. W. Iloltzout of thin br.ass spirals with a 

 thin coating of gelatine on one side. Independently, M. Nodon, 

 iif Paris, has constructed some recording hygrometers having 

 spirals made of Bristol board coated on one side with gelatine 

 (with a little salicylic acid), and on the other with bitumen. The 

 jirinciple is not new : in various collections of physical apparatus 

 similar arrangements have existed for at least a dozen years. 



Lenses which magnify, and yet are perfectly flat on both sides, 

 have been constructed by Schott and Co., of Jena, the manu- 

 facturers of Abbe's optical glass. These lenses are mere 

 curiosities. T hey consist of single disks of glass, such that the 

 refractive index tlecreases in a regular manner from the surface 

 inwards. The properties of this arrangement have been investi- 

 gated by Prof. K. Exner, of Vienna. 



Quadrant electrometers have been lately described by M' 

 Ledeboer, in which the motion of the needle (often of very 

 annoying duration) is damped so as to be aperiodic. This is 

 achieved by making each of the four "quadrants " of steel 

 highly magnetised. The needle is therefore damped by magnetic 

 friction. The suspension is unifilar. 



Several modifications have been lately introduced into the 

 I eclanche battery. Mr. Sydney Walker proposes to substitute 



sulphur for the manganese : it is cheaper, and less of it is 

 required. Mr. A. Pollak does away with the manganese, but 

 employs a special, porous, coarse, annular block of carbon, which 

 stands half out of the liquid and absorbs oxygen from the air to 

 depolarise. M. Germain introduces a novel material to hold the 

 liquid, an absorbent preparation, chiefly cellulose, made from 

 cocoa-nut fibre, and wliich has received tlie curious name cf 

 " cofferdam." It has truly remarkable absorbent properties, as 

 it will suck up and hold from twelve to fourteen times its own 

 weight of water. A "cofferdam" cell dees not spill the 

 liquid. 



Dry portable cells appear to be coming into favour, gelatine 

 being the favourite medium. They are claimed as novelties both 

 in Paris and in Frankfort. Joule's "glue-battery" — a Daniell's 

 cell, having a gelatinous mass impregnated with sulphates of 

 copper and zinc — is the parent of all these later forms. 



Electric welding is the latest of the industrial applications 

 of electricity, and it would seem to have already reached a tho- 

 roughly practical stage. Prof. Elihu Thomson, of Lynn, Massa- 

 chusetts, has shown that bars of iron, steel, copper, and brass can 

 be welded firmly together in a few seconds by passing through 

 their junction a very powerful electric current. He has invented 

 a special kind of transformer or induction coil to enable him to 

 accomplish this operation. It is possible thus to weld iron and 

 brass together in a firm joint. Simultaneously, researches on the 

 same subject have been made by two Russian gentlemen in the 

 laboratory of M. Marcel Deprez in Paris, and they have an- 

 nounced their discovery under the name of " electrohephaest." 

 If we are not mistaken, similar experiments were made before 

 the Academic des Sciences some years ago by the late M. 

 Ruhmkorff. Moreover, in Mr. J. P. joule's papers he mentions 

 the discovery of the practicability of electric welding by himself 

 and Sir William Thomson. 



According to Olszewski, the critical temperatures of nitrogen 

 and o.vygen are respectively - 146", - 118 '8', of the Centigrade 

 scale. 



ON THE MORPHOLOGY OF BIRDS ' 

 'T'HERE are several things that go to increase the interest in 

 ^ the morphology of these culminating Sauropsida at the 

 present time. 



(1) The discovery by Gegenbaur, Hu.xley, and others, of the 

 close relationship of birds and reptiles, especially of the extra- 

 ordinary fact that the hind-limb and pelvis of even the most 

 minute bird pass through a stage in which they correspond 

 almost exactly with the hind-limb and pelvis of the most 

 gigantic kinds of extinct reptiles — the Dinosaurs or Ornilho- 

 scelida. 



(2) The recent discoveries of biologists as to the composition 

 of the cheiropterygium in the various types of air-breathing 

 Vertebrata. It is now well known that the five-fingered hand 

 and the foot with five toes are the specialised modern repre- 

 sentatives of hands and feet that had at least seven rays in their 

 composition. 



And (3) the study of the development and general morphology 

 of birds is at the present time of great interest, now that we 

 are looking to the study of metamorphosis for some initial 

 elucidation of the mystery as to the origin of the various types 

 of Vertebrata. 



The labour of each succeeding day at this culminating class 

 makes it more and more impossible for me to conceive of birds 

 as arising direct from the Dinosaurians, or indeed from any other 

 order or group of reptiles. 



Long attention to the metamorphosis of the Amphibia has 

 intensified this difficulty to me ; for the newly- transformed frog 

 or newt appears to me to be the true counterpart of a newly- 

 hatched reptile — snake, lizard, turtle, or crocodile. 



Each of these young creatures, whether it has undergone a 

 true metamorphosis or has been the subject of pre-natal trans- 

 formation, is evidently an imago, although an imago that con- 

 tinues to grow. 



Now each amphibian has its own larva, for the larvae of the 

 various species have their specific differences. 



The thousand known species of existing Amphibia— Anurans, 

 Urodeles, and Csecilians — and all the lishes that undergo meta- 



' Paper W Prf.f. W. K. Parker, F.R S., read before the Royal Society on 

 January 27, 1887. 



