i8o 



NA TURE 



[December 20, igcx) 



The momentary gleams of the electric light-play can be very 

 easily observed by holding an albumen paper print thoroughly 

 well self-dried on glass, paper side downwards, in a perfectly 

 dark room over a hot room-stove to produce the paper's separa- 

 tion, and by stripping the print off downwards as sojn as some 

 edge of it has grown loose enough^probably with some sigris 

 of light— to allow it to be t iken in the fingers. I have by this 

 means now seen those brush and glow lights' flitting beams a 

 second time, and there seems to be no difficulty of producing 

 them in varied form and brightness by this method of pro- 

 ceeding. A. S. Herschel. 



Observatory House, Slough, December lo. 



Photography of the Static Discharge. 



The accompanying photograph of the spark of a large static 

 machine may possibly be of some interest to the readers of 

 Nature. The machine is a large lloltz, used in the electrical 

 department of St. Bartholomew's Hospital. It consists of eight 

 glass plates of twenty-nine inches in diameter, inclosed in a 

 glass case. It is driven by a motor which is worked by the 

 100 volt alternating main which supplies the electrical depart- 

 ment with its alternating current. The initial charge is ob- 

 tained from a small Voss machine which is inclosed in the case 

 of the Holtz. The photograph was obtained in the following 

 manner. The machine was started and the brass knobs of the 

 conductors adjusted to give a spark of about seven inches m 

 length. The knobs were now tested in the usual way (by pre- 

 senting a metallic point to the conductors) with reference to the 



sign of their charge. A gelatine dry plate was then taken, 

 inclosed firstly in an orange and then in a black envelope. The 

 plate was placed between the knobs of the conductors in a line 

 parallel with them and the sparks allowed to play over the 

 envelope for a period of one second of time. The plate was 

 then taken to the dark-room, developed and fixed in the 

 oidinary way. The accompanying illustration shows the curious 

 results obtained, A distinct break can be seen in the continuity 

 of the sparks between the positive and negative poles. Round 

 the positive pole the sparks are rushing off in a dense mass with 

 a direction from the negative pole of the machine. At the line 

 of separation of this dense mass of sparks is seen a depression 

 as if the mass had been eroded by the negative charge, remind- 

 ing one very forcibly of what happens to the positive carbon of 

 the arc light. At the negative pole the sparks are much less 

 dense and more fan-shaped, and radiate in the reverse direction 

 to the positive sparks with the exception of a cone of sparks, 

 which are much smaller, which approach the depression in the 

 positive mass. This prolongation of small sparks towards the 

 positive pole is seen in each of the photographs obtained. The 

 results of the experiment are curious. I am unable to explain 

 t^em, but think they are perhaps worthy of record. 



St, Bartholomew's Hospital. Hugh Walsham. 



Malaria and Mosquitoes. 



As I was reading the very interesting article by Dr. Fielding- 

 Ouldon the "Malaria Campaign," which appeared in Nature 

 of November 8, I was struck by the fact that the use of the 

 mosquito-netting he suggests as an efficacious preventive against 



NO. 1625, VOL. 63] 



malaria fever was already arrived at several years ago through 

 nothing but experience in one of the malaria districts in Syria, 

 The following is a translation of a letter published in vol. viii, 

 (April 1884) of the} ^W/^/aifa/, an Arabic literary and scientific 

 review, edited in Cairo, Egypt, by Drs. Sarruf and Nimr : — 



" To the Editors of Al-Muktataf. 



" Gentlemen, — I have already had the chance of observing 

 the spread of the malaria fever in Rashiya, both in the autumns 

 of 1878 and 1883, and I noticed that one of the principal agents 

 in effecting its spread was the mosquito. I have also noticed 

 that all those who, at the time of the epidemic, took pre- 

 cautions against the mosquito bites escaped the fever, a fact 

 well known in this part of the country. I therefore conclude 

 that mosquito nets which completely cover the bed and prevent 

 the entrance of mosquitoes are the best fever preventives in 

 countries abounding in malaria marshes. 



Abdella Jabbour, 



Rashiya. 



Trusting the above will find a place in your esteemed paper, 



N. Y. Sarruf. 

 Cairo, December 7. 



Can Spectroscopic Analysis Furnish us with Precise 

 Information as to the Petrography of the Moon? 



Theoretically I think we may reply in the affirmative, but 

 whether our means of observation are, as yet, delicate enough 

 to give give us trustworthy results I leave to the investigation of 

 your readers. 



As the question is of considerable interest, pardon me if I 

 enter somewhat into detail. 



(i) If we had two smooth, plane, parallel mirrors, perfectly 

 elastic, and a gas jet midway between them, we might first light 

 the gas and then extinguish it without destroying the illumina- 

 tion, for, if the mirrors were perfectly elastic, the waves of 

 light would oscillate between the two for ever with undiminished 

 intensity. We know that this is not the case, therefore no 

 known substance is perfectly elastic, 



(2) If direct solar light fall upon a large mass of sandstone, 

 part of it penetrates the mass as heat, and part is reflected, with 

 a diminished velocity, so that we might expect, a priori, an 

 apparent displacement of the Fraunhofer lines, as compared 

 with the spectrum of direct sunlight. 



(3) Similar results might be looked for with regard to lime- 

 stone, basalt, &c., but not identical, unless we make the very 

 improbable supposition that all solids are equally elastic. 



(4) Hence it should be possible to construct a table of 

 relative photo-elasticities so that if the substance were given its 

 elasticity might be found by inspection, and vice versd, 



(5) Next, analysing the sunlight reflected from various regions 

 of the moon, and referring to our table, we might hope for 

 answers to the questions 



(a) Are Tycho, Copernicus and the Appenines basaltic ? 



()3) Is the Mare Tranquilitatis the dried-up limestone bed of a 

 saltwater ocean, or the dried-up sandstone bed of a freshwater 

 inland sfea ? 



I admit, at once, that the observations suggested are of 

 extreme delicacy, but I cannot consider them insurmountable in 

 an age which has witnessed the proof of the regression and 

 subsequent approach of Sirius to the solar systetn by this very 

 method. W. J. Knight, 



Cork, 



INTERNATIONAL CATALOGUE OF 

 SCIENTIFIC LITER A TURE. 



AT the International Conference which met in London 

 last June to discuss this subject, it was thought 

 that the time had arrived when the great work of pub- 

 lishing a complete catalogue of all the scientific literature 

 of the world might be undertaken with every prospect 

 of success. 



A Provisional International Committee was, therefore, 

 appointed at the Conference to carry out the preliminary 

 work, and this Committee reported the results of its 

 labours to an International Council which met last week 

 in the rooms of the Royal Society, 



