May 19, 1 881] 



NA TURE 



CJ 



minimum. The worked-out exercises show that the mode 

 of working is easy of apprehension and leads to correct 

 results. A merit of the book, for frequent use, is that it 

 is handy in form and very clearly printed. 



LETTERS TO THE EDITOR 

 [ The Editor does not hold himself responsible for opinions expressed 

 by his correspondents. A'either can he undertake to return, 

 or to correspond with the writers 0/, rejected manuscripts. 

 No notice is taken of anonymous communications. 

 [The Editor urgently requests correspondents to keep their letters 

 as short as possible. The pressure on his space is so great 

 that it is impossible other-wise to ensure the appearance even 

 of communications containing interestins: and novel facts.'\ 



The so-called " Bunsen-Pump " 



Prof. Roscoe, President of the Chemical Society of London, 

 in enumerating the works of his fiiend Prof. Bunsen, says, in 

 Nature of the 28th ult. ("Scienlific Worthies," vol. xxiii. 

 p. 600) :— 



" To him we are also indebted for the apparatus for accelerat- 

 ing filtration, the 'Bunsen-pump,' together with all its appliances, 

 now employed in every laboratory." 



This assertion requires correction. The pump used by Prof. 

 Bunsen for accelerating filtration was invented by me, and not 

 by Prof. Bun«en, as would appear from the use of his name in 

 connection with it. I dejcribed the constiuction of the " water- 

 air-pump " distinctly and plainly in the Journal of the Chemical 

 Society of London fcr January, 1S65, under the title, "Re- 

 searches on the Vacuum : L The Instruments " (not the instru- 

 ment, as some will read), and I sent a copy of this paper to 

 Prof. Bunsen, inscribed with a suitable allusion to our former 

 relationship as pupil and teacher, during the spring of 1865. 

 Three years later Prof. Bunsen published his paper, "On the 

 Washing of Precipitates," in which he described again my pump, 

 but unfortunately omitted to quote my pafcr 0/1865. 



The following is a translation of Prof. Bunsen's own words : — 



" To create the difference of pressure for filti-ation one cannot 

 employ any of the air-pumps corcmonly u.ed, especially not the 

 mercury-air-pump, as the hquids to be filtered contain not 

 uiifrequently chlorine, suli'hurous acid, sulphuretted hydrogen, 

 and other substances, which would destroy the metallic portions 

 of the apparatus. I therefore employ a water-air-pump con- 

 structed of glass on the principle of Sprengel's mercury-air- 

 pump, which for all chemical purposes is, as I believe, preferable 

 to every other apparatus for air rarefaction, where it suffices to 

 push the rarefaciion no further than to a pressure of mercury 

 from 6 to 12 millimetres " {Ann. Chem. Pharm., lS68, vol. cxlviii. 

 p. 277). 



The peculiar stress laid here on the uselessness of mercury-air- 

 pumps, and on the fact that chlorine attacks mercury, combined 

 with the omission of all reference to my paper, where both -vafcr 

 and glass are mentioned, gave to Prof. Bunsen's description of 

 the instrument a colour of originality which Prof. Roscoe (and 

 with him many others) thinks right to support and to perpetuate 

 by calling it the " Bunsen-pump." 



As this misnomer has been already the subject of a disclaiirer 

 from Prof. Bunsen (Naturk, vol. vii. p. 241), of reiron trances 

 both from myself (vol. vii. p. 241), from Prof. Frankland 

 (vol. xiv. p. 74), and frtm others, I am sorry to see that Prof. 

 Roscoe should con inue to use this designation, which is in- 

 tended to honour an "employer" of the in. tiument, which hurts 

 the feelings of its inventor and deprives him of his only reward 

 — the satisfaction of being credited with having placed a useful 

 servant at the disposal of cience and industry. 



If any other inventor less eminent than Prof. Bunsen had 

 made the omission which I have pointed out with much reluc- 

 tance, no one would persist in s,iving his name to my child, 

 nor (reversing the case) wruld anybody speak of a pump as 

 " Sprengel's pump," if I had received from Prof. Bunsen the 

 paper of 1S65 and said in 1868, " I therefore employ a water- 

 air-pump constructed of glass on the principle of Bunsen's 

 mercury-air-pump." H. Sprengel 



Savile Club, London, May 7 



[I have read the foregoing note of expostulation from Dr. 

 Sprengel, and I regret that I have hurt his susceptibiUties. That 

 Dr. Sprengel first enunciated the principle both of the water- and 

 of the mercury-air-pump no one can doubt. But that Bunsen 



devised a water-pump suitable for filtration there can be as Utile 

 doubt. Hence in speaking of a " filter pump" — as every chemist 

 knew I was doing — as contradistingui-hed from an "air-puuip," 

 I conceive that I am justified in using the words " Bunsen- 

 pump." — H. E. ROSCOEJ 



Tide-Predicting Machines] 



The recent discussions respecting tide-predicting machines 

 have called to mind a very old invention of my own, which, 

 although originally desig,ned for a different purpose, seems to 

 me ca| able of solving the required problems with all attainable 

 accuracy. 



I communicated to the British Association at Cambridge in 

 184S " A description of a Machine for finding the Numerical 

 roots of Equations and Tracing a variety of useful Curves." 

 An abstract of that paper may be found at pages 3, 4, of the 

 Transactions of the sections. About the same time I litho- 

 graphed for private distribution a more detailed account of the 

 proposed machine, illustrated by diagrams. It begins with the 

 remark that "Persons engaged in testing theory by experiment 

 have frequently derived great assistance from mechanical con- 

 trivsnces, which give rapid and near approximations without 

 the trouble, in every separate case, of gcing through tedious 

 multiplications and additions. The proposed machine would be 

 capable of giving values of 2{* cos (k9 + o)}, or of tracing the 

 curve p = 2 {^ cos («6 -f o)}." 



At page 2 it is shown how it » as proposed to trace the curve 

 p — a Jr b cos («9 -H o). It is then remarked that, in the same 

 way, it w ould be possible to trace the curve p = 3 + /5 cos 

 (hB -f a) + /5, cos (K,e -f o,) -I-'*; cos {_n^9 -I- a,^, &c. Then 

 follow a variety of suggestions for the practical use of the 

 instrument, and at page 7 there are the following su^e»tions for 

 the construction of a n achine : — 



" As toothed wheels cannot be employed to turn the circles 

 (/4]), {A.;^, &c., I have m.ide use of a combination of the endless 

 screw and toothed wheels so that the error of the wheels is 

 almost destroyed. /p{Fig.) representsa handle attached to an axis 

 on which are mounted toothed wheels /, /., t^ . . . which gear w ith 

 the wheels 7", T^, &c., mounted on separate axe=, each having a 

 portion of a very accurate screw. These act on the circuni- 

 ferences of the circles (,-/,) {.-I,), &c., and cause them to revolve uni- 

 formly, as i.T Rams den's dividing engine, &:c." The large diagram 

 shows four of these [A) circles each of which gives one term, 

 i cos («fl + a), and these terms are ^ummed by the help of a 

 chain, such as is used to wind up watches, pns-ing over pulleys 

 carried by frames free to oscillate in parallel directions. I inclose 

 copies of the lithographed desciiption of the instrument. 



May 9 F. Bashforth 



Sound of the Aurora 



In Nature, vol. xxiii. p. 4S4, one of your correspondents 

 speaks of the sound of the aurora as " crackling," or as that of 

 "the flickering of blazirg fire," while another describes it as 

 hke the "rutling or switching of silk." On Monday, April 12 

 last, there was an electric storm here, and at 7 p.m. when I 

 walked home (the blazing lightning leaving but momentary 

 tntcnals of darkness), 1 heard all round me the constant crackling 

 or rustling of blazing flames. Towards the north-we-t across a 

 low .arc near the horizon pale sheet lightning swayed quickly to 

 and fro. There was no rain at the time, that came heavily 

 afterwards. The sound of flames was close round me, and 

 others had the same experience. No one I can find has ever 

 seen lightning so completely fill the air or heard such strange 

 sounds. F. C. Constable 



Karachi, April 25 



Meteorological Bibliography 

 I AM compiling a classified 1 ibiiography of meteorolosical 

 science, and being desir. us of rendering it as full as possible, I 

 should feel much obliged if you would intimate to meteorologists 

 that by sending copies of their papers to me they would do much 

 towards helping on the work. The publication of this; biblio- 

 graphy has already commenced in " The ScieLtific Roll.' 

 6, Kent Gardens, Ealing, W. A. Ra.MSAY 



An Optical Illusion 

 There is an exquisite optical phenomenon of which I (and 

 doubtless many others too) would be glad to see a really scientific 



