March 6, 1890] 



NATURE 



417 



says (p. 60) that he " was informed " (which implies that he 

 did not previously know) that " one of Van der Waals' papers . . . 

 contains an elaborate study of the molecular pressure in fluids." 



Again he says, " I have left the passages . . . which refer to this 

 subject in the form in which they stood before I became ac- 

 quainted with Van der Waals' work. I have not sufficiently 

 studied his memoir to be able as yet to form a definite opinion 

 whether the difficulty . . . which is raised in Appendix E. can, 

 or cannot, be satisfactorily met by Van der Waals' methods." 



Further, he states that he "had been under the impression 

 . . . that Laplace's views had gone entirely out of fashion — 

 having made, perhaps, their final appearance . . . about 1850." 



As a matter of fact. Van der Waals adopted Laplace's views 

 in 1873, and his formula diflfers from the expression /z' == RT, 

 only by the introduction of two terms, one of which is obviously 

 an additional pressure such as is deduced from Laplace's theory. 



I do not think that any reader could be expected to conclude 

 from these passages in Prof. Tait's Addendum that when writing 

 the paper he had long known the " main features of Van der 

 Waals' investigation." To me they seemed to mean that he had 

 not previously been acquainted with Van der Waals' work, nor 

 with his methods, nor with the facts that he studied molecular 

 pressure and adopted Laplace's ideas. 



While, therefore, I willingly submit to Prof. Tait's correction 

 of the phrase that he had " never heard of Van der Waals," I 

 cannot admit that, on the evidence then before me, I did him any 

 substantial injustice. 



(2) I very much doubt whether the distinction between the ulti- 

 mate volume and the molecular volume can be maintained if the 

 equations are treated as empirical ; and even if they are not, I 

 doubt whether the ultimate volume, as defined by Prof. Tait, has 

 any real physical meaning. The value of v when / — 00 is inde- 

 pendent of the temperature, whether deduced from the theoretical 

 formula to which Prof. Tait refers (p. 48), or from those of Van 

 der Waals or Clausius : hence it must (from this point of view) 

 be the molecular volume. In the case of Prof Tait's new 

 equation, which was published after his Report was completed, 

 and which is the only one I had not seen when I wrote the 

 review, the results when we put / = 00 or T = o, are such as to 

 show that its application to these extreme cases is not legitimate. 

 My own view is that such algebraical solutions are worth very 

 little, and I only discuss them because I wish to show that if we 

 admit them at all they justify my treating Prof Tait's number as 

 an estimate of the molecular volume. 



(3) I cannot say that I think that Prof. Tait's reason is 

 adequate. The Royal Naval College at Greenwich has done 

 more for our naval officers than he would have us believe, and, 

 if it were not so, the Challenger Reports are not addressed to 

 members of any one profession, nor intended for English-speak- 

 ing scientific men alone. Their cosmopolitan character is shown 

 by the fact that bound up in the same volume with Prof. Tait's 

 Report is another by a distinguished Belgian geologist. 



Foreigners have helped to describe the specimens which our 

 Expedition collected; they will read the Reports which our experts 

 have written. It would have required but a few minutes' work, 

 and a few additional lines of print, to have given the final 

 results in terms which they would have understood at a glance. 



(4) The analogy is fallacious. Prof. Tait has devise:! a 

 formula into which he introduces two quantities (age and speed), 

 which are commonly expressed with reference to different units 

 of time. 



I pointed out that he had expressed in the same formula (con- 

 trary to common usage) the same quantity (pressure) in terms of 

 two different units, of which one is not ordinarily used by 

 many of those who will make use of his work. 



As to the last paragraph, I have only two remarks to make. 

 First, that I think Prof. Tait does himself injustice in re- 

 garding a description of apparatus devised by another, and the 

 discovery of a blunder of the Bureau International, as two of 

 the most important things in his Report. Secondly, that I 

 think the imputation of motives should be banished from 

 scientific discussions. 



In conclusion, I wish to add that probably I should have left 

 Prof. Tait's defence unanswered if he had not accused me of 

 unfairness, I have no desire for any controversy, and no wish 

 to impugn his knowledge of the theory of gases. But he will 

 forgive my reminding him of the old saying, *' Noblesse oblige." 

 A classical research should not be published in a state which 

 leads the reader to the conclusion that the author was only just 

 becoming acquainted with facts which bear upon his work and 

 have been long before the world. As a reviewer, I formed the 



opinion that the Report under discussion was open to this 

 criticism. As a reviewer, it was my duty to express my opinion 

 in all honesty, and, as I hope, in all courtesy. 



Arthur W. Rucker. 



Visualized Images produced by Music. 



In the annexed paper, and in her own words, are related the 

 very curious effects produced on a lady friend by certain musical 

 tones and orchestral combinations. They are so very singular, 

 so entirely outside my experience, and, withal, so inexplicable, 

 that I shall be glad if you will give them a place in your 

 columns, in the hope that some of your readers — physiological 

 or psychological — may be able to throw some light on them. 



I should state that the lady is in perfect health, is very intelli- 

 gent, an accomplished musician, and not at all, in this or any 

 sense, the victim of a disordered imagination. She is quite 

 conscious that these spectral images have only a subjective exist- 

 ence, though visually they have all the vividness of presentment 

 which belongs to realities. 



At the first blush it would seem as though these apparitions 

 were in some way a response to stimuli sent through the auditory 

 nerve ; but this, if any, is an imperfect explanation, since it will 

 be noticed that occasionally these visualized pictures slightly 

 precede the instrument they belong to. 



This fact suggests that a state of unconscious expectancy may 

 be a factor in their reproduction, but it fails entirely, I think, to 

 account for their initial appearance. Geo. E. Newton. 



25 Woodland Road, Gipsy Hill, S.E. 



" The sound of an oboe brings before me a white pyramid or 

 obelisk, running into a sharp point ; the point becoming more 

 acute if the note is acute, blunter if it is grave. The obelisk 

 appears to be sharply defined and solid if the note is loud, and 

 vague and vaporous if it is faint. All the notes of the 'cello, 

 the high notes of the bassoon, trumpet, and trombone, and the 

 low notes of the clarionet and viola, make me see a flat un- 

 dulating ribbon of strong white fibres. 



"The tone of the horn brings before me a succession of white 

 circles of regularly gradated sizes, overlapping one another. 

 These circles and the ribbon float past me horizontally, but the 

 point of the obelisk seems to come at me. 



" In an orchestra, when the violins strike up, after the wind 

 band has been prominent for a time, 1 see often, but not always, 

 a shower of bright white dust or sand, very crisp and glittering. 

 I am taking note of the recurrence of this impression, and think 

 it is becoming more frequent, but it is not invariable like the 

 others. 



" I have heard a great deal of orchestral music all my life, 

 but I have only noticed these effects for four or five years. They 

 gained gradually in frequency and clearness, and now the first 

 three are invariable. 



" If I know the scoring of a piece well, the various effects 

 slightly precede the instrument they belong to ; only the objects 

 are vague and faint till the sound begins. 



" Sometimes, if an oboe passage has an intense and yearning 

 character, the white point comes so near me, and moves so 

 rapidly, that I think it must wotmd tiie. 



' ' I am very anxious to make it clear that I am not trying 

 to describe a mental state by symbols, but that / actually see 

 the point, the fibres, and the circles. Generally they seem to 

 float half-way between me and the orchestra. 



"If only one class of instruments is used, the effect does not 

 extend beyond the opening bars : for instance, in a string 

 quartette I only see the white sand for a moment at the begin- 

 ning ; if, however, wind and stringed instruments are combined, 

 I see the various effects again and again in one piece." 



Foreign Substances attached to Crabs. 



In your issue of December 26, 1889 (p. 176), Mr. Pascoedrew 

 attention to the cases of certain crabs which are frequently found 

 covered with sponges, algae, shells, &c., and brought forward 

 also the well-known case of the Gastropod Phorus. He at the 

 same time confessed that he could not see " where protection 

 came in" in any of the cases which he cited. Mr. A. O. Walker, 

 on the other hand (Nature, January 30, p. 296), regards it as 

 obvious that the attachment of these foreign substances is a 

 useful adaptation for purposes of concealment. Pn if. Herdman 

 also (Nature, February 13, p. 344) bears witness to the 



