Sept. 9, 1875J 



NATURE 



399 



only for practical purposes, but also from a theoretic point 

 of view, to compare the consumption of zinc during the 

 generation of the current with that in the unconnected bat- 

 tery, as theory alone gives no basis on which to decide 

 the question whether the zinc disssolved in the uncon- 

 nected battery is entirely, partly, or not at all used in the 

 connected battery for the generation of the current. In- 

 vestigation showed that the quantity of zinc dissolved in 

 the disconnected battery is a little under half of the con- 

 sumption of zinc necessary acording to theory to generate 

 the current in the connected battery, and that only a part 

 of the metal dissolved in the disconnected battery without 

 current-generation is used up in the connected one for 

 the generation of the current. This fact entirely corre- 

 sponds with the view that the dissolution of the zinc 

 must not be looked upon as the cause of the current, but 

 as a necessary condition of the same. Investigation 

 further showed that while in the chromic acid battery 

 above desciibcd, on the average only 22 per cent, of 

 zinc was lost, the loss in the nitric acid battery expe- 

 rimented with was 48 per cent, on the average. The 

 chromic acid battery without clay cells is the least 

 constant one amongst the ordinary constant batteries. 

 But if used in a proper manner it may serve for a 

 very long time. Prof. Bunscn possesses a battery of 

 this kind, of forty pairs, with an active zinc surface on 

 each plate of only forty square cm. For the last eight 

 lecture-terms it has served for all experiments without 

 its having been necessary during this long time to renew 

 the zinc plates, or their coatings of wax, or the original 

 exciting hquid, nor to clean the conducting connection 

 parts ; it has been merely necessary to renew now and 

 then the amalgamation of the zinc plates (an operation 

 which only takes a few minutes of time) and to replace 

 that part of the liquid which was lost by evaporation in 

 the air, by simply filling the cylinders with water up to 

 the marks on their sides. The apparatus to this day 

 still gives an electric arc between carbon points which 

 amply suffices for the photo-chemical lecture experiments. 

 The currents obtained by this battery, which has now 

 been in use for already more than four years, are still 

 powerful enough for demonstrations in electrolysis, spark 

 spectra, decomposition of gases by induction sparks, 

 &c., and will doubtless continue to suffice for all these 

 purposes for some time to come. But we must again 

 repeat that effects of such magnitude can only be ex- 

 pected if the precaution is used (and it is very easy to do 

 so) not to leave the pairs in contact with the liquid for 

 one moment longer than the duration of the current 

 necessary for the experiments requires it. 



The battery used for the production of spark spectra 

 consists of four of the pairs above described. The pole 

 wires conduct the primary current, of which a branch 

 puts the current interrupter into action, to a Ruhmkorff 

 apparatus, the induction coil of which has a diameter of 

 nearly 0-2 metres and a length of 0-5 metres. The cur- 



rent induced in the same is conducted to the spark appa- 

 ratus, standing in front of the slit of the spectroscope : 

 a, a Ijottle with three necks, serves as a stand for the 

 spark apparatus. The induced current goes from the 

 mercury cup b, through the fine wire c to the carbon point 

 d, which is fastened on a pointed platinum wire ; thence 

 it passes as a spark to the other carbon point e, and from 

 this it reaches the second mercury cup f, which is con- 

 nected with the other end of the induction coil. The 

 platinum wires, which are surrounded by glass tubes 

 sealed firmly upon them, can be moved upwards or down- 

 wards by the corks h, and this allows of a quick and 

 exact fixing of the carbon points before the slit of the 

 spectroscope. 



The carbon points destined to receive the little quanti- 

 ties of liquids under, examination are best prepared from 

 the ordinary and not too light drawing charcoal, which 

 is easily procurable. In order first to impart con- 

 ducting power to the charcoal, a great number of the 

 sticks are exposed to the most intense white heat for 

 some time in a covered porcelain crucible, which stands 

 in a larger clay crucible, and is on all sides surrounded 

 by charcoal powder. Then the sticks are cut to points at 

 one end, and the little charcoal cone thus obtained is 

 cut off with a fine watchmaker's saw. In order to re- 

 move the silica, magnesia, manganese, iron, potash, soda, 

 and lithia which the charcoal contains, about a thous and of 

 the points are boiled in a platinum dish, first with hydro- 

 fluoric acid, then with concentrated sulphuric acid, then 

 with concentrated nitric acid, and finally with hydro- 

 chloric acid, repeating each process several times, while 

 between each manipulation each of the acids is removed 

 by washing and boiling with water. After this treatment 

 the carbon points are ready for use. A carbon cone of 

 this description weighs about o'oi5 grammes, and can 

 absorb more than its own weight of liquid. The spark 

 spectra obtained by aid of them are of very long duration. 



We will report on the second part of Prof. Bunsen's 

 treatise as soon as it has been published. W. 



HISTORICAL NOTE ON THE OBSERVATION 

 OF THE CORONA AND RED PROMINENCES 

 OF THE SUN* 



SO much interest attaches to the phenomena of the 

 corona and red prominences, as observed during 

 total solar eclipses, and correct views of their nature and 

 of the proper means of observing them are so recent, that 

 I feel it proper to give here a brief account of what I 

 believe to be the first attempt to see these, under ordinary 

 conditions, with an uneclipsed sun.f This account is con- 

 tained in the private diary of the late G. P. Bond, formerly 

 director of the Observatory of Harvard College, which 

 has become known to me through the kindness of his 

 daughters. 



Bond observed the total solar ecHpse of July 28, 1851, 

 at Lilla Edet in Sweden, and his report is published in 

 the Memoirs of the Royal Astronomical Society, vol. xxi., 

 p. 97. 



From Sweden, Bond went to Geneva, where he arrived 

 in September 1851, and from this point I may transcribe 

 from his diary, making no changes except the occasional 

 insertion or omission of unimportant words. 



" Geneva, Sunday, Sept, 14, 1851.— I think I must go 

 to Chamounix to try whether it may be possible to discern 

 the red flames on the sun's disc by occulting all but the 

 very edge, upon one of the lofty peaks. It seems to me not 

 altogether impossible. Certainly an experiment worth 

 trying and a new application of the 'Aiguilles.' . . . 



'•'■Geneva, Sept. 15, 1851. — ... The weather looks 

 dark and lowering, with an uncomfortable north-east 



• By Edward S. Holdcn. Reprinted from the August number of the 

 Amerkiiii Journal of Science. 



\ Airy, Nasmyth, Baden-Powell, Piazzi-Smyth, and others experimented 

 in this direction, about this time, with various results. See Edinburgh Ast. 

 Obs., vol. xi. p, 279 ; Mem. R. A. S., vol. xvi. p. 301, &c. 



