74 



NA TURE 1^ 



[Sept. 2. 1875 



were placed at his disposal by Messrs. Chance Brothers, of 

 Birmingham, the question may perhaps be considered as settled. 

 After some preliminary trials, a piece of glass free from strix 

 was prepared of titanate of potash mixed with the ordinary 

 ingredients of a crown glass. As the object of the experiment 

 was merely to determine in the first instance whether titanic acid 

 did or did not confer on the glass the universal property of 

 separating the colours at the blue end of the spectrum materially 

 more, and at the red end materially less, than corresponds to a 

 similar dispersive power in ordinary glasses, it was not thought 

 necessary to employ pure titanic acid ; and rutile fused with 

 carbonate of potash was used as titanate of potash. The glass 

 contained about seven per cent, of rutile, and as none was lost, 

 the percentage of titanic acid cannot have been much less. The 

 glass was naturally greenish from iron contained in the rutile ; 

 but this did not affect the observations, and the quantity of iron 

 would be too minute sensibly to affect the irrationality. 



Out of this glass two prisms were cut. One of these was 

 examined as to irrationality by Prof. Stokes, by his method of 

 compensating prisms ; the other by Mr. Ilopkinson, by accurate 

 measures of the refractive indices for several definite points in 

 the spectrum. These two perfectly distinct methods led to the 

 same result, viz., that the glass spaces out the more as compared 

 with the less refrangible part of the spectrum no more than an 

 ordinary glass of similar dispersive power. As in the phosphatic 

 series, the titanium asserts its presence by a considerable increase 

 of dispersive power ; but, unlike what was observed in that 

 series, it produces no sensible effect on the irrationaUty. The 

 hopes therefore that had been entertained of its utility in silicic 

 glasses prepared for optical purposes appear doomed to 

 disappointment. 

 y A paper was read by Mr, J. A. Fleming, Oit the Decom- 

 / position of an Electrolyte by Magneto-electric Induction. When 

 a solid conductor is moved in a magnetic field induced currents 

 are created in (it. In a solid these expend themselves partly 

 or wholly in producing heat in the conductor. The paper was 

 occupied with an examination of the effect produced on electro- 

 lytes under the same circumstances, viz., when made to flow 

 or move in a magreiic field : experiments were described to 

 show first that induced currents are produced under these condi- 

 tions in electrolytes, and then that the electrolyte is to some 

 extent decomposed by these currents. / 



Dr. Moffat, in his paper On the apparent comiection between 

 Sunspots, Att>iospheric Ozone, Rain, and Force of Wind, stated 

 that in discussing ozone observations from 1850 to 1869, he had 

 observed that the maxima and minima of atmospheric ozone 

 occurred in cycles of years, and that he had compared the 

 number of new groups of sunspots in each year of these cycles 

 with the quantity of ozone, and the results showed that in each 

 cycle of maxima of ozone there is an increase in the number of 

 new groups of sunspots, and in each cycle of minima a 

 decrease. He also gave a table to show that the years of 

 maximum ozone and number of sunspots were generally 

 distinguished by an increase in the quantity of rain and the 

 force of the wind. 



Sir W, Thomson's paper On the effectsof Stress upon the Mag- 

 netism of Soft Iron was a continuation of two that had been read 

 before the Royal Society. In the physical laboratory at Glas- 

 gow University he had stretched steel and soft iron wire about 

 twenty feet long from the roof. An electro-magnetic helix was 

 placed round a few inches of the wire, so that the latter could 

 be magnetised when an electric current was passed through the 

 former ; the induced current thus produced in a second helix 

 outside the first being indicated by a reflecting galvanometer. 

 "When steel wire was used, the magnetism dimmished when 

 weights were attached to the wire, and increased when they 

 were taken off ; but when specially made soft iron wire (wire 

 almost as soft as lead), the magnetism was increased when 

 weights were put on, and diminished when they were taken off. 

 Afterwards he discarded the electrical apparatus, and by suspend- 

 ing a piece of soft iron wire near a magnetometer consisting of a 

 needle, a small fraction of a grain in weight, with a reflecting 

 muTor attached, the wire was magnetissed inductively simply 

 by the magnetism of the earth, and changes in its magnetism 

 were made by applying weights and strains, the changes being 

 then mdicated by the magnetometer. 



Prof W. F. Barrett read a paper On effects of Heat on the 

 mtitcul^r structure »f Stet Wins and Rods, in the course of 



which he said he found that if steel of any thickness be heated 

 by any means, at a certain temperature the wire ceases to 

 expand, although the heat be continuously poured in. During this 

 period also the wire does not increase in temperature. The length 

 of time during which this abnormal condition lasts varies with 

 the thickness of the wire and the rapidity with which it can be 

 heated through. It ceases to expand, and no further change 

 takes place till the heat is cut off. When this is done the wire 

 begins to cool down regularly till it has reached the critical 

 point at which the change took place on heating. Here a 

 second and reverse change occurs. At the moment that the ex- 

 pansion occurs, an actual increase in temperature takes place 

 sufficiently large to cause the wire to glow again with a red-hot 

 heat. It is curious that this after-glow had not been noticed 

 long ago, for it is a very conspicuous object in steel wires that 

 have been raised to a white heat and allowed to cool. 



Mr. Braharn exhibited some experiments on magnetised rings, 

 plates, and discs of hardened steel, and also experiments on air, 

 hydrogen and oxygen. 



SECTION D. 



Biology, 



Opening Address by Dr, P, L. Sclater, M.A., F.R.S. , 

 F.L.S., President. 



On the Present State of our Knowledge of Geographical Zoology. 



In the office, which I hare now held for more than sixteen 

 years, of Secretary to the Zoological Society, of London, I have 

 been not unfrequently requested by our members and correspon- 

 dents in various parts of the world to furnish them with infor- 

 mation as to the best works to be consulted on the zoology of 

 the countries in which they are respectively resident, or which 

 they are about to visit. With the well-furnished library of the 

 Zoological Society at my command this is not usually a very 

 difficult task, so far as publications are actually in existence to 

 supply the desired information. I am also frequently asked to 

 ^point out the principal deficiencies in our knowledge of ihe ani- 

 mals of particular countries. This is also a not very difficult 

 request to reply to, although it is somewhat embarrassing on ac- 

 count of the very imperfect information which we still possess of 

 geographical zoology generally, and the largeness of the claims 

 1 am therefore constrained to put forward for the attention of 

 those who make such inquiries. Great, however, has been the 

 progress made of late years towards a more complete knowledge 

 of the faunas of the various parts of the world's surface. Expe- 

 ditions have been sent out into countries not previously explored ; 

 collections have been formed in districts hitherto little known ; 

 and many general works have been published, combining the 

 results of previous fragmentary knowledge on this class of sub- 

 jects. Under these circumstances I have thought that such an 

 account as I might be able to give of the general progress that 

 has been recently made towards a better knowledge of the zoology 

 of the various parts of the earth's surface, accompanied by a 

 series of remarks upon the best available authorities to be con- 

 sulted upon such subjects, might supply a want which, as above 

 mentioned, I know by personal experience is often felt, and at 

 the same time would form a not inappropriate address from the 

 chair which I have now the honour to occupy. 



I must premise, however, that my observations must be re- 

 stricted mainly to the terrestrial members of the sub-kingdom 

 Vertebrata, To review the recent progress of our knowledge of 

 the various sections of invertebrate animals in different countries 

 would be beyond my powers, and would inordinately enlarge my 

 subject. Besides, it is certain that the higher classes of animals 

 have occupied the principal attention of recent writers on geo- 

 graphical zoology, and it is with their distribution that we are 

 best acquainted. 



Taking, therefore, the seven great regions into which the 

 earth's surface may be most conveniently divided for zoological 

 purposes one after another, I will endeavour to point out our 

 leading authorities on the Mammals, Birds, Repriles, Batrachians, 

 and I'ishes of each of them, and their main constituent parts. 

 At the same time, I will endeavour to indicate the principal de- 

 ficiencies in our knowledge of these subjects, and may perhaps 

 be able to add a few suggestions as to how some of these defi- 

 ciencies might be best overcome. 



In these remarks I will take the divisions of the earth's surface 



