458 



J^A TURE 



[February 17, 1910 



of chance, moreover, it generally happens that two meet- 

 ings occur with just an interval of one day between them, 

 which makes it still more difficult to attend either. 



Would it not be possible to fix one day, namely, Friday 

 afternoon and evening, as a general day of meeting for the 

 societies? This would, I feel sure, allow many provincial 

 members to come down to London for the occasion, partly 

 because they could merge the Friday with their " week- 

 end," and partly because they might have the chance of 

 attending several meetings the same afternoon and even- 

 ing. I doubt whether such an arrangement would incon- 

 venience many of the London members ; but, even if it 

 does, the London members might perhaps be willing to 

 give way, because to them, in any case, attendance is much 

 more easy than it is to men who live perhaps hundreds of 

 miles away. I have discussed the matter with several 

 friends in Liverpool, all of whom seem to be favourably 

 impressed with the idea. Ron.'VLd Ross. 



Johnston Tropical Laboratory, University of 

 Liverpool, February 5. 



The Meaning of " lonisation." 



In his interesting notice concerning the work of 

 Arrhenius, published in Nature of February 3, Prof. 

 Walker, in a somewhat ambiguous manner, refers to " the 

 notion and practical definition of degree of ionisation " as 

 the great positive contribution of the distinguished 

 physicist. " Whatever be our views of the origin and 

 nature of ions, we must "... — he says — " have recourse 

 to the notion of degree of ionisation." It is a little difficult 

 to see how we are to have recourse to a notion if we are 

 not clear what view that notion is based upon and includes. 

 To appreciate Prof. Walker's position, it is essential that 

 we should know precisely what meaning he attaches to 

 the words I have quoted — what conception underlies them. 

 I would beg Prof. Walker to tell us, in clear, unmistakable 

 terms, what exactly he would have us understand by the 

 word ionisation. 



When the Royal Society has completed its Catalogue of 

 Scientific Papers of the last century, it will doubtless be 

 compelled to prepare a dictionary in explanation of the 

 terminological inexactitudes to be found in its Proceedings 

 and other journals ; of these, ionisation will be one of the 

 most difficult to interpret. Prof. Walker will render real 

 service if he will tell us in what sense or senses he uses 

 the word throughout his notice ; does he or does he not 

 use it as connoting explicitly the separation of a substance 

 in solution into several portions, each capable of acting 

 as a distinct kinetic unit? This, I believe, was the 

 doctrine enunciated by .'\rrhenius in 1887, and which, if I 

 mistake not, he still professes. Does Prof. Walker 

 advocate such doctrine? 



Henry E. Armstrong. 



Prof. Armstrong and I look at ionisation from different 

 points of view. He is chiefly interested in an interpreta- 

 tion of the process and phenomena of ionisation in terms 

 of the kinetic molecular theory. I am chiefly concerned 

 to have a theory, whatever be its exact mechanical inter- 

 pretation, which is capable of being mathematically formu- 

 lated and of acting as a guide in quantitative investigation. 

 My position, in short, is that of the astronomer who is 

 content to have Newton's law for practical purposes, and 

 only takes a speculative interest in theories of the nature 

 of gravitation. 



Possibly the best analogue in physics to Arrhenius 's 

 theory of electrolytic dissociation is van der Waals's theory 

 of the continuity of the gaseous and liquid states. Van 

 der Waals's theory can be put in the form of a compara- 

 tively simple equation which is very successful in repre- 

 senting the facts in broad general outline, though in many 

 cases it proves to be imperfect in detail. Although the 

 kinetic molecular assumptions on which van der Waals 

 based his theory may be questioned, his equation will 

 remain an important aid to investigation in its special 

 domain until it is superseded by another of comparable 

 simplicity and of greater comprehensiveness. 



James Walker. 

 NO. 2103, VOL. 82] 



The Invention of the Slide Rule. 



In Nature of January 13 (p. 307) Dr. Alexander Russell, 

 in writing of the invention of the slide rule, says ; — " Sup- 

 porting the latter view is the fact that he (Oughtred) pub- 

 lished (1633) his ' Mathematicall Recreations ' under the 

 pseudonym of Henry Van Etten." This evidently implies 

 that Oughtred was the author of the said " Mathematicall 

 Recreations," whereas the very title of the work shows 

 that it was a translation, and not an original contribution. 

 •It reads : — " Mathematicall Recreations ; or a collection of 

 sundrie problemes and experiments in arithmeticke, cosmo- 

 graphie, astronomic, architecture, chimistrie, &c., ex- 

 tracted out of the ancient and moderne philosophers, ho-lU 

 delivered into English tongue with the examinations, correc- 

 tions and augmentations by W. Oughtred." 



The italics are ours. The translation was made from the 

 French of Henry Van Etten 's " Recreation Mathematique, 

 composee de plusieurs problemes, plaisants et facetieux, 

 en fait d'Arithm^tique, Geometrie, Mecanique, Optiq. ; et 

 autres parties de ces belles Sciences." The accents are 

 missing in the ti'le-page. The work was published in Paris 

 in 1624. The name of Henry Van Etten is indeed a 

 " pseudonym," but it is that of Jean Leurechon (1591— 

 i6qo), a French Jesuit of uncommon mathematical versa- 

 tility, and not that of William Oughtred (1574-1660), an 

 English divine of no less uncommon mathematical abihty. 

 Brother Potamian. 



Manhattan College, New York City, January 27. 



Transit of Halley's Coinet. 



Mav I point out that at the time of the transit of 

 Halley's comet the sun will be above the horizon at the 

 North Cape? The Cape is distant 18° 49' 20" from the 

 pole, and the declination of the sun at midnight of May 18 

 will be 19° 31' 42"; adding 27' 22" for refraction, the 

 sun's altitude at midnight would be 1° 9' 44", and the 

 altitude would increase before the first contact, which will 

 take place, at i6h. 6m. local time. The Cape rises to a 

 height of 968 feet, and there should be a very fair sporting 

 chance of seeing something of whatever there may be to 

 see during the sixty minutes' duration of the transit. 



C. S. Taylor. 



Banwell Vicarage, Somerset, February 11. 



Dangerous Lecture Experiments. 



.Although it is no part of my duty to teach chemistry, 

 I have on several occasions had to perform an experiment 

 which Mr. Marie quotes (p. 428) as being dangerous, viz. 

 the collection of hydrogen from the action of sodium on 

 water. I can fully endorse his warning. Twice a violent 

 explosion took place; but I found that if the piece of 

 sodium is carefully cleaned so that all its surfaces are 

 bright, and cold water used, the experiment can be carried 

 out in safety. I do not know if these important details 

 have found their way into the practical manuals in use 

 in chemical laboratories. If not, I trust that this experi- 

 ment is not one that beginners are directed to make. 



M. D. Hill. 



Eton College, Windsor, February 11. 



Aged Tadpoles. 



Last year I reared about five thousand tadpoles, and, 

 dividing them into twenty portions, brought most of them 

 to the frog stage. As they matured, and the numbers be- 

 came smaller, the survivors were gradually brought 

 together again into a few vessels, finally into one. Of 

 those which were in the tadpole stage in November, none 

 changed to frogs. They died one by one until only two 

 are left. These are quite healthy — active feeders with long 

 tails and hind legs, but no appearance of fore legs. 

 Perhaps some of your readers will be able to say whether 

 it is usual to have tadpoles a year old, and whether one 

 may expect any change to take place now — whether, 

 perhaps, like Axolotl, they may not exhibit the power of 

 reproducing their own kind if they remain alive. 



j!oHN Don. 



Carrick Academy, Maybole, N.B. 



