i6o 



NA TURE 



[Da. 1 6, 1880 



Survey of India, made some valuable observations on certain 

 points connected with soil-formation, &c., in Central Asia. 



Under the title of "Die geographische Erforschung des 

 afrikanischen Continents von den altesten Zeiten bis auf 

 unsere Tage," by Dr. Philipp Paulkt^chlce, Messrs. Brockhausen 

 and Brauer of Vienna have published a volume of 320 pages, 

 containing a brief but full sketch of tlie progress of African 

 exploration from the earliest times down to the present day. Its 

 special value consists in the detailed bibliography of the subject 

 contained in the footnotes on every page, which must be of 

 the greatest service to the student of African exploration and 

 geography. There are occasional slips, as when Mr. Monteiro's 

 book ou "Angola and the River Congo" is entered under 

 "Monteiro," as published in New York in 1875, and again 

 under "J. John," as published in London in 1876. But such 

 blunders are wonderfully few. About 1500 names are referred 

 to altogether. 



Dr. Lenz, on November 22, was at St. Louis, whence he 

 was going to Tangier. 



As a memorial of the work performed in the Vega, a " Vega 

 Fund " has been raised by subscription in Sweden to encourage 

 further geographical research. The sum raised is 35,000 crowns, 

 which will be intrusted to the Swedish Acidemy of Sciences, 

 and the interest either employed at once or be allowed to accu- 

 mulate for a term of years. Only natives of Sweden, Norway, 

 Denmark, and Finland will be entitled to receive the benefit of 

 the fund. 



Two important expeditions are soon to be sent into Central 

 Africa, under the auspices of the Algerian Missionary Society, 

 which already has stations at the northern ends of Lake Tan- 

 ganyika and the Victoria Nyanza. One will go from Zanzibar, 

 and the other will ascend the Congo. 



THE INFLUENCE OF PRESSURE AND 

 TEMPERATURE ON TPIE SPECTRA OF 

 VAPOURS AND GASES' 



T N the course of my inquiry last year into the homology of the 

 •*• spectral lines of chemically-related elements I occasionally 

 made the observation that the two strongly-marked red lines 

 which bromine in the fluid state gives when the spark is taken 

 from it in De la Chanal's fulgurator grow very feeble or entirely 

 disappear in the spectrum of the rarefied vapour in the Geissler- 

 tubes, while other lines not previously seen become visible. It 

 appeared to me of interest to inquire more particularly into the 

 changes of the spectrum of one and the same element, as these 

 changes are naturally of the greatest importance in the com- 

 parison of chemically-related elements ; and with this view I 

 addressed myself to the problem of the changes of spectra at 

 higher pressures, 



.. According to WuUner's well-known experiments, which only deal 

 with the three permanent gases, hydrogen, oxygen, and nitrogen, 

 the spectral lines of the second order grow broader with higher 

 pressure, and at the same time a continuously illuminated back- 

 ground is to be observed. This phenomenon, however, presents 

 even in the three permanent elements the greatest difference. 

 Thus, while the lines in the hydrogen spectrum become easily 

 i)roader even under moderate pressure, those in the spectrum 

 of nitrogen do not expand. Therefore it occurred to me that a 

 comparative investigation, which would extend to as many 

 elements as possible, would be desirable, inasmuch as it en- 

 couraged the hope that by this means one could arrive at a law, 

 perhaps even at an explanation, of these phenomena. 



I now venture to present to the Academy a report of my 

 experiments as far as they have gone, reserving a full account 

 till their completion. 



In my experiments I have treated the most volatile of the 

 metalloids, and among the metals have included quicksilver 

 and sodium. I will in due time give a full account of the 

 apparatus and methods -Hhich I employed in my experiments, 

 but at present I must confinp myself to a statement of the results 

 already ascertained. 



The spectrum of the three halogens, at higher pressures, ex- 

 hibits in each case the same peculiarities. The lines have the 

 appearance of merging into each other, and without showing 



1 Sitz. Bcr. der k. Ahad. der IFiss., Vienna, Ix.xvii. 



an expansion into bands, they become occasionally somewhat 

 broader. There is a steadily luminous background which 

 becomes brighter when the pressure is increased, and which 

 is often more intense than the lines themselves. This latter 

 circumstance is frequently seen in the case of iodine, where 

 the continuous spectrum finally covers all the rett. In the case 

 of chlorine and bromine single lines are always distinguishable 

 from the continuous surrounding light. The appearance of 

 certain lines in the red field in chlorine and bromine which 

 always preserve their precision and delicacy is worth mentioning. 



The changes in the intensity of the spectral lines as exhibited 

 under different pressures are very interesting. If you compare 

 the spectral lines of the halogens with each other, in order to 

 ascertain their homology, and in doing so only employ the spectra 

 of rarefied vapotu-s in Geissler tubes, you meet considerable diffi- 

 culties, for you can only compare the lines in groups, and these 

 lines present frequently in each of the three elements such differ- 

 ences of intensity that yon may be left in doubt as to the existence 

 of a homology of their lines. But the apparent differences arise 

 in reality out of the variation of intensity and the number of 

 the lines with the pressure. By appropriate change in the 

 density of the gas or vapour you can always produce spectra 

 which exhibit the perfect homology of the lines. Thus, in the 

 case of iodine you must employ that tension which iodine-vapour 

 has at 50° or So° C, while in the case of chlorine and bromine 

 atmospheric pressure is required. 



The spectrum of sulphur does not change at all at higher 

 pressure, the lines maintaining their perfect sharpness, while in 

 the red field a continuously illuminated background appears. 



Phosphor and arsenic do not give any reaction, and even the 

 continuous spectrum does not appear. With arsenic I observed 

 what I think has hitherto been overlooked, namely, that it gives 

 at a moderate pressure, and without the interposition of a 

 Leyden jar, a spectrum of the first order. It is almost con- 

 tinuous, and with increase of pressure of interposition of the 

 jar it gives to the spectrum of lines the spectrum of the second 

 order. 



Great is the difference between the metalloids of which v/e 

 have hitherto been speaking and the metals ; they show an ex- 

 pansion of their lines into bands, while the continuous light takes 

 a less prominent place. In quicksilver the breadth especially 

 of the green and violet lines is conspicuous. 



With sodium I have only noticed the great width of the D- 

 lines when they appeared reversed, for I could only examine the 

 light after its passage through a layer of cooler vapour. Sodium 

 gives at high pressures a continuously illuminated spectrum near 

 the D-lines, which then appear reversed ; at first one or two 

 lines, but soon they widen and merge into each other, and the 

 dark band of absorption gradually covers the whole illuminated 

 part of the field. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE 



Cambridge. — Prof. Stuart finds the progress of his School of 

 Mechanism and Engineering again compels enlargement. Some 

 pupils are now making small engines, and require more space for 

 erecting thtm. A room for mechanical drawing is needed, andalso 

 an enlarged stove. The Museums and Lecture-rooms Syndicate 

 think it best in the present condition of University funds to 

 erect a new temporary building 46 feet long by 21 feet wide, 

 adjacent to the present workshop, and this, with other rooms 

 which can be added, will supply present necessities for about 

 360/. 



The balance of 821/., being the debt on the last two years of 

 the Museums Maintenance Fund, has been granted as an extra 

 payment from the University Chest, and in future years 3000/. 

 will be granted ^annually for the Museums and Lecture-rooms 

 Maintenance Fund. 



Prof. Stuart is to have the services of a Demonstrator of 

 Mechanism and Applied Mechanics. 



Clare College announces a scholarship of 60/. a year in 

 chemistry and chemical; physics, botany and geology, to be 

 competed for on March '29 next, without limit of age. Jesus 

 and Magdalene Colleges continue to offer no inducements to 

 natural science. 



By a Royal decree, published last month, a museum will 

 shortly be opened at Palermo on the plan of the one founded in 

 Rome in 1S74, with the object of making known the best Echo- 



