214 



NATURE 



[Jtine 20, 1878 



A few yeai-s ago yet another theory was started, based on M, 

 Quincke's discovery of the tendency of liquid films to expand 

 rapidly upon wetable surfaces. The only advantage of this 

 lay in accounting for the rapidity of the rise of sap ; otherwise it 

 was open to all the objections of the Jamin theory. 



A theory has lately been propounded, and thoroughly worked 

 out, by M. Joseph Bohm, which is characterised by good con- 

 sistency, and offers perhaps a more satisfactory explanation of 

 the phenomenon than any that have been referred to. It is 

 based, like the osmotic theory, on the cellular structure of all 

 sap -conducting plants, and it attributes an important rdle to the 

 elasticity of the cells. " When the surface-cells of a plant," says 

 M. Bohm, "have lost a portion of their water through evapora- 

 tion, they are somewhat compressed by the air-pressure. Like 

 elastic bladders, however, they tend to take their original form. 

 This of course is only possible by their drawing in either air or 

 water from without. Since, however, moist membranes are 

 little penetrable by air, the cells draw from cells further in a 

 pjrtion of their liquid contents. These again borrow from their 

 neighbours further down, which contain more water, and so on, 

 either to the extreme root-cells or to those parts of the stem 

 which are supplied with water from below through root- 

 pressure." 



To illustrate the action M. Bohm constructed an artificial 

 cell-chain. A funnel closed by a bladder represented the 

 evaporating leaf ; to it were connected below several glass tubes 

 about two ctm. wide, closed at one end with a bladder, and 

 joined together in series by means of thick-walled caoutchouc- 

 tubing. In consequence of the evaporation, the membrane 

 which closes the funnel-mouth is bent inwards, and when it has 

 reached a certain tension water is sucked into the funnel out of the 

 next lower cell, which covers its loss in like manner. Manometers, 

 connected with certain cells of the apparatus, indicate the 

 amount of suction at different heights. To avoid fouling of the 

 membranes carbolic acid was- mixed with the distilled water in 

 the cells. Since bladder membranes, with a not very great 

 height of liquid column over them, admit passage of water by 

 filtration, these artificial cell-chains (it is pointed out) must act 

 much more imperfectly than the sap- conducting cells placed 

 over one another in living plants, which cells, by reason of their 

 narrow aperture, retain their liquid column by capillary attraction. 



It is shown that this theory is in harmony with sundry pheno- 

 mena which are contradictory of the imbibition theory. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE 



It will be proposed to confer the degree of D.C.L. honoris 

 causa at the ensuing Oxford commemoration, upon Dr. William 

 Spottiswoode, M.A., of Balliol College, F.R.S. 



The following awards for proficiency in Natural Science have 

 been made at St. John's College, Cambridge : — Foundation 

 Scholarships to F. J. Allen, Marr, Slater, C. M. Stuart ; 

 Exhibitions to Fleming, Hart ; the Open Exhibition to C. H. O. 

 Curtis, from the Royal School of Mines. 



The plans for the new University edifices at Strasburg have 

 just been completed. They provide for over loo rooms to 

 serve as auditoriums, museums, the inevitable German singing 

 hall and fencing hall, &c., and will meet the needs of all sections 

 of the university, with the exception of the medical faculty, which 

 retains its old quarters, on account of the propinquity to the 

 hospital. The attendance, which has fallen off during the past 

 year, is now greater than ever before, the number of students 

 for the present semester being 710. 



SCIENTIFIC SERIALS 



Journal de Physique, April. — In this number M. Vincent re- 

 commends chloride of methyl as a frigorific agent, and indicates 

 an abundant source of it. He employs a cylindrical copper vessel 

 having double walls, between which the liquid is admitted 

 through a peculiar cock from an adjoining vessel. In the central 

 part is put an uncongealable liquid such as alcohol. The outer 

 wall is enveloped in cork. On opening the cock the chloride of 

 methyl enters into ebullition, and the temperature of the alcohol 

 bath sinks to — 23°. By connecting with an air pump and 

 making vacuum, a much lower temperature may be obtained. 

 One pretty experiment with this apparatus is the crystallisation 

 of mercury. — M. Gariel explains the new system of numbering 



glasses of spectacles, in which a unit called the dioptrie -is 'used, 

 this being the power of a convergent lens of im. focal distance. 

 The number of dioptrics for a particular lens is got by dividing 

 im. by the focal distance reckoned in metres and decimal frac- 

 tions of a metre, since the power varies in inverse ratio of the 

 focal distance. Let Nd be the number of a lens reckoned in 

 dioptrics and ^„ the focal distance in metres, then NdTj,^. = im., 

 which gives one of the quantities when the other is known. — M. 

 Pellat contributes a mathematical paper on the specific heats of 

 vapours, and the phonograph occupies some attention, 



Meinorie della Societh degli Spettroscopisti Italiani, January, 

 1878. — Prof. Tacchini contributes a long paper on the appear- 

 ance and constitution of the sun, based on the photographs of 

 M. Jansen taken at Meudon ; there is also another by the same 

 author, giving the observations of the positions in which the 

 magnesium and 1474 lines appeared on the limb of the sun in 

 June, 1877. The appendix contains a paper by L, Gruber on 

 the falling stars of the first part of last November. 



February. — Notice of the death of Father Secchi, by the 

 editor. — A paper by Prof. Rosetti on the temperature of the 

 sun ; a description of the thermopile and the necessary acces- 

 sories, together with the results, is given at length. — A table 

 showing the number of spots and protuberances, and the heights 

 of the latter during the first half of the year 1877, and drawings 

 of the chromosphere for the months of November and Decem- 

 ber made at Rome, by Prof. Tacchini. 



March. — A note and table by Prof. Tacchini showing the 

 position on the sun's limb when the magnesium and 1474 lines 

 were seen during June, 1877. Also a summary of the positions 

 of the same during the first half 0/ the year 1877. 



SOCIETIES AND ACADEMIES 

 London 



Royal Society. — " Note on the Specific Gravity of the Va- 

 pours of the Chlorides of Thallium and Lead," by Henry E. 

 Roscoe, F.R.S. , Professor of Chemistry in Owens College, 

 Manchester. 



Experimental difficulties of so serious a nature surround the 

 attempt to ascertain the specific gravity of vapours at a high 

 temperature that, in spite of the interest which attaches to this 

 subject, but few additions have been made in our knowledge in 

 this direction since the researches of Deville and Troost. 



The present experiments, of which this notice contains the 

 first results, have been made with the object of so simplifying 

 the process as to render it easy to determine the specific gravity 

 of the vapours of bodies possessing high boiling points with a 

 degree of accuracy sufficient for the purpose of controlling their 

 molecular weights. 



The method consists in vaporising the substance under ex- 

 amination in long-necked glazed porcelain globes of known 

 capacity placed in a muffle raised to bright redness. The tem- 

 perature of the globe is ascertained by a calorimetric determina- 

 tion made with heavy platinum weights placed in the muffle, 

 this determination being checked by the simultaneous insertion 

 in the muffle of a second globe containing mercury. 



The porcelain globes having a capacity of about 300 cub, 

 centims., and containing from three to nine grams of substance, 

 are closed by loosely-fitting stoppers of baked clay, and then 

 gradually introduced in the muffle. After remaining there until 

 no further escape of vapour is observed, and until the tempera- 

 ture has become constant, the globes are quickly withdrawn 

 from the muffle and their contents removed and analysed, the 

 temperature being in each case ascertained by the calorimetric 

 method at the time of withdrawal of the globe. The following 

 determinations of the specific gravity of mercury vapour serve to 

 show the reliability of the method : — 



Experiment I. 

 11. 



„ in. 



„ IV. 

 V. 



Temperature 



determined 



calorimetrically. 



o 



... ICI9 ... 



Specific gravity 



of mercury 



vapour. 



... ... 6'92 



894 675 



815 6-91 



972 577 



1047 7-05 



the calculated specific gravity (Hg= 198*8) being 6728, 



Before determining the specific gravity of the vapour of 

 thallium chloride it was ascertained that this compound does not 



