486 



NA TURE 



[March 25, 1886 



referring to the abstract of M. Konovaloff's paper in the Journal 

 of the Chemical Society for January, i8S6, I meet with the follow- 

 ing : — " As an explanation of this contact-action phenomenon it 

 is asked whetlier it is not possible that the bombardment of the 

 molecides on the solid matter causes the kinetic energy of the 

 molecules to be transformed in part into the internal work re- 

 quired for their decomposition." 



Perhaps some of your correspondents will kindly furnish me 

 with references to original memoirs (or other sources of informa- 

 tion) in which I may find this question competently treated. 

 The idea here put forward by M. Konovaloff is surely not new. 

 It might lie extended, as I conceive, to such cases as, for 

 example, the combination of SO.j and O.2 to form SO3, the for- 

 mation of ammonia from a mixture of NO and H„ in the pro- 

 portion of 5H2 -^ 2NO, the formation of NO from a mixture of 

 NH3 with an excess of O.,, in each case when the gaseous mix- 

 ture is passed over heated platinum sponge or platinised asbestos. 

 For some years past this explanation of sucli contact-action 

 phenomena has appeared to me much more reasonable than such 

 explanations as are generally suggested. The hi^h temperature 

 required in such cases seems to point rather to something in 

 common with the initial dissociation caused by the intense heat 

 of the electric spark, when oxy-hydrogen gas is fired. In such 

 cases as those referred to above the lesser intensity of the heat 

 applied from without may easily be compensated by intra-mole- 

 cular results of the increased energy with which the impact of 

 individual molecules must take place at high temperatures, and 

 the great extension of the heated solid surface exposed to their 

 bombardment. Under this view (with which my pupils have 

 been familiar for some years past) combination is brought about 

 through the atoms of some of the molecules of the mixed gases 

 being brought into the ijuasi-nasceiit state. A. Irving 



Wellington College, March 10 



Variable Stars 



In Nature for March 11 (p. 440) Dr. Mills, in criticising 

 Prof. Seeliger's collision hypothesis of the blazing forth of Nova, 

 advances a theory of his own as a presumably original and novel 

 explanation of the phenomena of variable stars. It may be of 

 interest, therefore, to point out that practically the same ex- 

 planation was suggested in 1878 by Prof. R. Meldola in a paper 

 published in the Fhilosophical Magazine (or July of that year. 



In this paper the author states: "It is conceivable that in 

 certain cases the composition of a star's atmosphere may be such 

 as to permit a considerable amount of cooling before any com- 

 bination takes place among its constituents ; under such circum- 

 stances a sudden catastrophe might mark the period of combina- 

 tion, and a star of feeble light would blaze forth suddenly, as 

 occurred in 1866 to t Corona; Borealis. In other cases, again, 

 it is possible that the composition of a star's atmosphere may be 

 of such a nature as to lead to a state of periodically unstable 

 chemical equilibrium ; that is to say, during a certain period 

 combination may be going on with the accompanying evolution 

 of heat, till at length dissociation again begins to take place. 

 In this manner the phenomena of many variable stars may per- 

 haps be accounted for." 



It will be seen that these hypotheses are essentially identical, 

 although it would appear that Dr. Mills limits his explanation 

 to the formation of polymerides (presumably of some primordial 

 matter), these constituting our chemical "elements." I cannot 

 see, however, that he has any reasons for excluding the forma- 

 tion of true compounds, or why he should consider a variable 

 star as necessarily one that is engaged only in "making ele- 

 ments." This last process would, no doubt, be the first to take 

 place on the hypothesis of cooling from a state of complete dis- 

 sociation, but there would surely come a period w hen the more 

 stable chemical "compounds" could exist, and their formation 

 would also be attended by the evolution of heat and possibly of 

 light also. Jxo. Castell-Evans 



London, March 13 



The Iridescent Clouds and their Height 



Col. Tennant is mistaken in supposing that the only pecu- 

 liarity of the clouds which appeared in December 1S84 and 

 1885 is in their being fringed with coloured spectra, though 

 these were, I believe, much more vivid than those of ordinary 

 clouds, as described by him ; besides which, my impression was 

 that the colours were more varic.l than is usu.ally the case. Col. 



Tennant, with his experience, will be better able to say than I 

 am whether there is generally as much blue in the clouds 

 he describes as in those under discussion. I stated in my letter 

 of Dec. 29 last (p. 199) that there was no special amount of blue 

 in the clouds seen the previous day, but on the 31st there was 

 a good deal. However, I do not insist on this as being any 

 important difference ; but, by referring to the numerous letters 

 this year and last about the clouds, he will see there were 

 several other characteristic points. 



These clouds are not like any ordinary clouds ; if they can 

 be referred to any of the usual classes they are cirrus, but de- 

 cidedly different from any cirrus we generally see. Their usually 

 very smooth texture was striking, though some on December 28 

 (1885) had the oidinary appearance of rippling, but in most 

 cases this was too slight to be visible without optical aid, even 

 when the clouds were broken up into narrow wisps, and in such a 

 position that no colour was produced there was still some- 

 thing in their appearance which struck me as different from 

 ordinary clouds. The frequently rectangular shape was very 

 singular also, though they had not always this form. I said I 

 had not observed this shape in the clouds of December 28, but 

 other observers noted it on that occasion (see pp. 219, 220), and 

 on the 31st I saw many of the clouds with this outline. It is 

 shown indistinctly and with the corners cut off in Mr. C. 

 Davison's sketches (pp. 292, 293). The form is generally de- 

 scribed in the letters you have published as rhomboidal, but this 

 is an effect of perspective ; no doubt if the clouds were seen 

 overhead they would appear rectangular. Their great height, 

 too, must have been unusual, though perhaps not greater than 

 that of the singular coloured clouds seen last summer in Bavaria 

 by myself and in this country by others, as described in 

 Nature, and which differed from the clouds I am now describ- 

 ing in some important particulars. One patch of cloud was ob- 

 served both here and at Shields on December 28, and a calcula- 

 tion from a comparison of the position as seen from the two 

 places gives its height as 23 miles ; while making the ut- 

 most allowance that seems permitted for the roughness of the 

 observations only reduces its elevation to il miles. That it 

 was the same patch of cloud observed from both places is un- 

 doubted, for one observer of it (H. R. Procter) was travelling 

 from Shields to Sunderland, and he saw that it was the same 

 patch all the time, and the one I had been observing here. The 

 fringes of colour were distinctly visible on this cloud up to 

 4h. 25m., and feebly so till 4h. 27|m. I concluded that the sun 

 had not ceased shining upon it till that time ; if so, its height 

 would be between II and 12 miles. At 4h. 28.2m. it was pink 

 with sunset colouring ; but the sun need not have been shining 

 on it then. 



The iridescent colours have no connection with halos, as sup- 

 posed by Mr. Stone (p. 391), no particular colour appearing at 

 any particular distance from the sun, but every colour being seen 

 at any distance, though more vividly at perhaps from 15° to 30° 

 off the sun. Tiios. W. Backhouse 



Sunderland, March 12 



Forms of Ice 



A CURIOUS formation has lately occurred on the surface of a 

 sheet of ice in a tub. Being under a tap, the ice became sub- 

 merged below several inches of water. Fresh ice then formed 

 as thin vertical plates upon, and at right angles to the submerged 

 sheet. These plates meeting each other in all directions, pro- 

 duced a spongy mass, 3 or 4 inches thick. I do not know if it 

 is a common production, but the special interest attached to it is 

 that it would seem to suggest how "spongy" quartz has arisen, 

 of which I have a specimen consisting of thin and nearly parallel 

 plates ; as well as the well-known form of thin crystalline plates 

 in which calcite may occur. It is just this form of calcite 

 which gives rise to "hacked" quartz, when silica has coagu- 

 lated or crystallised over a mass of such thin crystals, and then 

 these latter have been subsequently dissolved out. 



Why a sheet of ice should increase regularly in thickness by 

 additions to its lower surface, and form this spongy mass on its 

 upper, is a question I should like to hear solved. 



Another form of ice I lately noticed on a wall consisted of 

 minute prisms standing in little depressions in the bricks. 

 The circumference of the prism partook of tlie irregular form of 

 the cavity, giving the appearance of an upward growth. 



While speaking of ice, I should like to venture a suggestion 

 to account for its lighter specific gravity than that of water, 

 namely, that water crystallises in macles of complex form ; the 



