NA TURE 



[April 24, 1902 



With VVilhelmy's apparatus, and much which he con- 

 structed for himself, often out of the simplest materials, 

 he was able to exhibit many of the chief optical expjri- 

 ments which could at that time be seen nowhere else out 

 of Paris, and to inspect which some of the leading men of 

 science in lierlin, such as the mathematician Kronecker, 

 were glad to visit him. To take but one instance of his 

 ingenuity in devising efficient substitutes for the com- 

 plicated and expensive forms of apparatus generally used, 

 we may mention his method of constructing a Fresnel's 

 double mirror. Two equal plates of black glass are 

 fastened to a suitable wooden slab by means of 

 four wax pellets, two under the corners of the 

 adjacent edges, and one each under the centre of the 

 opposite ends of the plates. If now a thin sheet of glass 

 is laid over the whole and gently pressed down in the 

 centre, the two glass plates become inclined to one 

 another at slightly less than 1 80^, forming — expcrto crede 

 —a perfect Fresnel's mirror. In this way the students 

 in his present " Praktikum " construct this piece of 

 apparatus for themselves as required. 



Quincke's settlement in Berlin was signalised by his 

 discovery of the " Stnimungsstnime," or electric cur- 

 rents produced by the flow of liquids past solid walls, 

 which is the inverse phenomenon to the '• elektrische 

 Fortfiihrung," or transport by an electric current of sus- 

 pended particles through liquids in narrow channels. 

 This he examined in an extensive research, leading to 

 the conclusion that both phenomena were due to electri- 

 fication by contact of the liquid with the solid wall or the 

 siispended particles. The range of cases in which elec- 

 trification is produced by contact of dissimilar substances 

 was thus largely increased, and inter alia it was shown 

 that a bubble of air in contact with water carries a 

 negative charge, a result which accounts for the interest- 

 ing discovery of Lenard that in the neighbourhood of 

 Alpine waterfalls the air is invariably strongly negatively 

 charged. 



To this same period belong two extensive series of 

 researches in optics and capillarity respectively. The 

 optical investigations, recorded in close upon a score of 

 lengthy papers in Poggendorff's Annakn, deal with the 

 most difficult questions connected with the optical proper- 

 ties of metals, the researches of Cauchy, Stokes and 

 Jamin, and the behaviour of polarised and diffracted light 

 in general. From among the results obtained we have 

 only space to mention the discovery of " lamellar dif- 

 fraction," ' the proof that neither Jamin's law of polarisa- 

 tion by reflection nor Stokes's theory of the polarisation 

 of diffracted light is m accord with all the facts, the 

 considerable addition to the theory of the diffraction 

 grating, and the startling deduction from some of the 

 work of the fact (long afterwards confirmed by Kundt 

 and others) that the refractive index of silver and gold 

 for sodium light is less than i, a result which of course 

 means that light travels faster through these metals than 

 in air. It is an interesting fact that these researches 

 were originally prompted by the hope of penetrating more 

 deeply into the secrets of the molecular constitution of 

 matter. Many of them were carried out by the help of 

 thin metallic films deposited on glass. I>ut these very 

 films did not a little to show that capillary phenomena 

 were likely to be more fruitful in this direction. One of 

 the most elegant of modern researches is that in which 

 (1869) he used a wedge-shaped film of silver deposited 

 on glass to measure the range of molecular attraction, 

 by determining the thickness of the silver film through 

 which the capillary action of the glass on water in con- 

 tact with the plate just vanished. The result was that 

 the radius of the sphere of action of the molecules is about 

 50 /ifi (i.e. about one-tenth of an average light- wave). 

 This was the first effective attack on this profoundly in- 



• Precht ((f,Vr</. .4«,. Ixi.) believes he has found .i similar phen^mirnon in 

 tne case of ROntgen rays. 



NO 1695, VOL. 65] 



teresting problem; the method remains the least excep- 

 tionable yet devised, and the result has been confirmed 

 by the later researches of Sohncke (iSgo)," though 

 Riintgen and others, by means of more questionable 

 methods, have found a value many times smaller. 



It will be convenient to speak of the capillary researches 

 in a general view presently, but mention must be made 

 here of the well-known acoustic interference tube. The 

 invention of this (1866) was due to a case communicated 

 to him by a doctor, in which a patient, whose hearing 

 was being tested by [sounding a tuning-fork at the end 

 of a rubber tube leading to his ear, was found to hear 

 better when the tube was pinched. This was the first 

 of several forms of acoustic interference apparatus de- 

 vised by Quincke, which have been used by his pupils 

 for investigations on the velocity of sound under various 

 conditions, recently, for instance, in air at high tempera- 

 tures. From this research it appears that the ratio of the 

 specific heats for air falls from v i,o at o' C. to i'34 at 

 1000° C. 



In 1872 Quincke was appointed to the chair at Wiirz- 

 burg, whence he was called in 1875 to fi" Kirchhoff's 

 place at Heidelberg. His work there has been marked 

 by a long series of electric and capillary researches, 

 and by a great increase both in the efficiency of the 

 laboratory and in the number of students. Among those 

 who have studied under Quincke or worked in his 

 laboratory may be mentioned Profs. Lenard (Kiel), 

 Braun (Strassburg), W. Konig (Frankfort), Max Wolf 

 (Heidelberg), Precht (Hannover), and Willard Clibbs and 

 Michelson of America. The work is still hampered by 

 want of room and by the antiquated character of the 

 building, which compares but poorly with the " Paliiste 

 der Physik " recently erected at several of the German 

 Universities. But men are more than buildings, and 

 Quincke has shown astonishing ingenuity in utilising 

 the space and means at command to accommodate the 

 120 students who attend his " Praktikum." 



It is perhaps in association with the practical work of 

 his laboratory that Quincke is seen at his best. He 

 maintains a constant interest in the doings of his 

 " Praktikanten " ; no student is too dull nor any experi- 

 ment too simple to enlist his personal attention. His 

 research students find him unfailing in advice and assist- 

 ance of the most helpful kind. If he is on occasion 

 " heftig," it is only to become kinder and more helpful 

 than ever. He gives his time ungrudgingly to his 

 "Colloquium" and "Seminar." In the latter (held in 

 the summer .Semester) he lectures at length on some 

 classical research, the practical work in connection with 

 which is then carried out by the students, and the theory 

 reproduced and results recorded in full for his approval 

 and criticism. The Colloquium (in the winter Semester) 

 is a small society for the discussion of current physical 

 research. Here one learns to admire alike the patient 

 consideration he shows the '" \'ortragender " (even if the 

 latter happen to be a foreigner stumbling through his 

 task in the most deplorable (ierman), the independence 

 and originality of his own outlook on current theories, 

 and his extraordinarily wide acquaintance with both the 

 older and the most recent literature of physics. 



His lectures deal with an unusually wide range of 

 topics, and are illustrated, not merely by a large collection 

 of diagrams mostly drawn, and where necessary coloured, 

 by his own hand, but also by many experiments rarely 

 exhibited elsewhere. To cjuote a few instances almost 

 at random, it is not often that one has the opportunity of 

 seeing Cornu's hyperbolas (formed by reflection of mono- 

 chromatic light from the surface of a bent glass strip), or 

 water spread out in a capillary film on the surface of 

 mercury, or experimental proof of the fact that super- 



1 And by the investigation of R. Weber (1901) on oil films (referred 10 in 

 Prof. Rucker's recent presidential address), which was carried out in 

 Quincke's own laboratory. 



