July 3, 1890] 



NATURE 



229 



•malaria in a concentrated form ; that if there is a thick 

 screen of primeval forest or a grove of plantains between 

 the dwelling-place and a large clearing or open country 

 there is only danger of the local malaria around the 

 ■dwelling, which might be rendered harmless by the 

 slightest attention to the system ; but in the open country 

 neither a house nor a tent is sufficient protection, since 

 the air enters by the doors of the house, and under the 

 flaps, and through the ventilators to poison the inmates. 



" Hence we may infer that trees, tall shrubbery, a high 

 wall or close screen interposed between the dwelling- 

 place and the wind currents will mitigate their malarial 

 influence, and the inmate will only be subjected to local 

 ■exhalations. 



"Emin Pasha informed me that he always took a 

 mosquito curtain with him, as he believed that it was 

 an excellent protector against miasmatic exhala4;ions of 

 the night. 



" (2ueslion, might not a respirator attached to a veil, or 

 face screen of muslin, assist in mitigating malarious 

 effects when the traveller finds himself in open regions.''" 



As a matter of fact, we believe a veil or a mosquito 

 •curtain is found a useful preventive in malarial regions. 



Mr. Stanley gives some natural history notes which he 

 obtained from Emin. Here, for example, is a statement 

 ■which he gives in Emin's own words, but which notwith- 

 standing is somewhat astounding : — 



" The forest of Msongwa is infested with a large tribe 

 of chimpanzees. In summer-time, at night, they frequently 

 visit the plantations of Mswa Station to steal the fruit. 

 But what is remarkable about this is the fact that they 

 use torches to light the way ! Had I not witnessed this 

 extraordinary spectacle personally, I should never have 

 credited that any of the Simians understood the art of 

 making fire. 



" One of these same chimpanzees stole a native drum 

 from the station, and went away pounding merrily on it. 

 They evidently delight in that drum, for 1 have frequently 

 heard them rattling away at it in the silence of the night." 



The importance of this fact with regard to fire-using 

 (it is not stated that they are fire-making) chimpanzees 

 need not be pointed out. We cannot doubt the accuracy 

 of Mr. Stanley's report, nor the trustworthiness of Emin's 

 observation ; but we should like to have more details. 



Great expectations have been formed of Mr. Stanley's 

 narrative of one of the most remarkable African expedi- 

 tions on record. These expectations have not been dis- 

 appointed. The reader who merely seeks for the 

 excitement of adventure will find what he seeks in almost 

 every page. We have written enough to prove that the 

 student of science and the geographer will find the narra- 

 tive teeming with novel and suggestive facts. There are 

 no doubt a few marks of haste and fatigue on the part of 

 the author ; but the work is altogether worthy of Mr. 

 Stanley's brilliant record, and entitles him, let us once 

 more say, to be ranked among the foremost pioneers of 

 science in " Darkest Africa." 



By the courtesy of Messrs. Sampson Low and Co. we 

 are able to give a few specimens of the 150 illustra- 

 tions which add so much to the beauty and value of the 

 book, which from the point of view of get-up is entirely 

 creditable to all concerned. J. S. K. 



PROBLEMS IN THE PHYSICS OF AN 

 ELECTRIC LAMP.^ 



A T this stage it will perhaps be most convenient to 

 ■^^^ outline briefly the beginnings of a theory proposed to 

 reconcile these facts, and leave you to judge how far the 



' Friday Evening Discourse delivered at the Royal Institution by Prof. 

 J. A. Fleming,' M. A., D.Sc, on February 14, 1890. Continued from p. 201. 



NO. 1079, '^'OL. 42] 



subsequent experiments confirm this hypothesis. The 

 theory very briefly is as follows : — From all parts of the 

 incandescent carbon loop, but chiefly from the negative 

 leg, carbon molecules are being projected which carry 

 with them, or are charged with, negative electricity. I 

 will in a few moments make a suggestion to you which 

 may point to a possible hypothesis on the manner in which 

 the molecules acquire this negative charge. Supposing 

 this, however, to be the case, and that the bulb is filled 

 with these negatively-charged molecules, what would be 

 the result of introducing into their midst a conductor such 

 as this middle metal plate which is charged positively ? 

 Obviously, they would all be attracted to it and discharge 

 against it. Suppose the positive charge of this conductor 

 to be continually renewed, and the negatively-charged 

 molecules continually supplied, which conditions can be 

 obtained by connecting the middle plate to the positive 

 electrode of the lamp, the obvious result will be to pro- 

 duce a current of electricity flowing through the wire or 

 galvanometer, by means of which this middle plate is 

 connected to the positive electrode of the lamp. If, 

 however, the middle plate is connected to the negative 

 electrode of the lamp, the negatively-charged molecules 

 can give up no charge to it, and produce no current in the 

 interpolated galvanometer. We see that on this assump- 

 tion the effect must necessarily be diminished by any 

 arrangement which prevents these negatively-charged 

 molecules from being shot off the negative leg or from 



Fig. 8.— Collecting plate placed at end of a tube, 18 inches in length, 

 opening out of the bulb. 



striking against the middle plate. Another obvious 

 corollary from this theory is that the " Edison effect " 

 should be annihilated if the mietal collecting plate is 

 placed at a distance from the negative leg much greater 

 than the mean free path of the molecules. 



Here are some experiments which confirm this deduction. 

 In this bulb (Fig. 8) the metal collecting plate, v/hich is 

 to be connected through the galvanometer with the 

 positive terminal of the lamp, is placed at the end of a 

 long tube opening out of and forming part of the bulb. 

 We find the " Edison effect " is entirely absent, and that 

 the galvanometer current is zero. We have, as it were, 

 placed our target at such a distance that the longest range 

 molecular bullets cannot hit it, or, at least, but very few 

 of them do so. Here again is a lamp in which the plate 

 is placed at the extremity of a tube opening out of the 

 bulb, but bent at right angles (Fig. 9). We find in this 

 case, as first discovered by Mr. Preece, that there is no 

 " Edison effect." Our molecular marksman cannot shoot 

 round a corner. None of the negatively charged mole- 

 cules can reach the plate, although that plate is placed at 

 a distance not greater than would suffice to produce the 

 effect if the bend were straightened out. Following out 

 our hypothesis into its consequences would lead us to 

 conclude that the material of which the plate is made is 

 without influence on the result, and this is found to be 

 the case. Many of the foregoing facts were established 



