July 19, 1877] 



NATURE 



227 



the miracle of an astonishing progress." In the Funda- 

 mental Takimetry (introductory to Takitechny) objects 

 are classified into square, round, pointed, and truncated 

 forms. The three lessons of Takimetry are (i) equiva- 

 lence ; (2) resemblance ; (3) the three squares of a right- 

 angled triangle (i.e., " Euc.,' i. 47). The subject requires 

 only three lectures, each of an hour's duration. Amongst 

 the subjects for measurement are the accessible, the in- 

 accessible, and the incalculable (/.t'., those which depend 

 upon the circle). There is much that is good in this book, 

 though in its present form it is overweighted with a mass 

 of extraneous matter. By aid of the prettily-coloured 

 figures (there are models, also, we aie told, to accompany 

 the book) a considerable kno.vledge of mensuration, we 

 think, might be imparted even to dull boys. We could 

 take exception to the translation in many places. 



LETTERS TO THE EDITOR 



\The Editor does 710I hold himself responsible for opinions expressed 

 by his correspondents. Neither can he undertake to return, 

 or to correspond with the writers of, rejected manuscripts. 

 No notice is taken of anonymous communications. 



The Editor urgently requests correspondents to keep their letters as 

 short as possible. The pressure on his space is so great that it 

 is impossible otherwise to ensure the appearance even of com- 

 munications containing interesting aiid novel facts. ] 



Museum Reform 



"J. P." suggests, under tlie head of " IVIuseum Reform" 

 (vol. xvi. p. 1S3), the idea of a conference of museum keepers, 

 out of which a permanent union among museum officers miglit 

 result. I am of opinion thai this idea is an excellent one, and 

 that the administration of the museums of all countries would 

 gain a great deal if an opportunity to museum officers were 

 offered to interchange their opinions and to communicate tu 

 each other their different practical experiences. Perhaps some 

 arrangements and rules might generally be accepted, as, e.g., 

 to labelling specimens, exchanging duplicates, publishing annual 

 reports in a journal ad hoc, &c. A. B. Meyer 



Dresden, July 9 



Koenig's Tuning-Forks 



Tllic letter of Ilerr Koenig inserted in Nature (vol. xvi. 

 p. 162) did not come under my notice till July 8. On October 27 

 last year I counted all the 64 sets of beats in Ilerr Appuim's 

 tonometer, one through 15, the rest through 20 seconds with a 

 pocket chronometer which was gaining less than 4 seconds a day, 

 and found every set of beats perfectly true. The perfection of the 

 consonances, more than So of which I tested laechanically, by 

 observing the beats that arose on flattening one of the two con- 

 sonant notes, seemed to me to eliminate all possible error of 

 irregular counting. The suggestion novsr is that the beats were 

 perfectly rej;ular and uniform, and that no exception need be 

 taken to my counting, but that Ilerr Appunn's pendulum was 

 originally incorrect, to such an extent that what appeared to him 

 So beats in 20 seconds, were only 79'27, andthatmy chronometer 

 was not sufficient to detect the error. If this were the case al! 

 the numbers on Herr Appunn's tonometer would have to Le 

 reduced by as nearly as possible 9 in 1,000, which would make 

 them agree with Ilerr Koenig's. I shall therefore have to re-test 

 the tonometer with a larger chronometer and if possible count 

 each set of beats for a longer time. I shall not be able to 

 undertake this examination at present, but I shall not neglect 

 doing so, and will inform you of the result. It is right, however, 

 to say that on July 9 and 10 I received communications from 

 Prof McLtod showing that his improved instrument for counting 

 vibrations gave results almost exactly agreeing with Herr Koenig's 

 numbers. The marked difference of Ilerr Appunn's and Ilerr 

 Koenig's numbers will I hope lead to such an examination of the 

 subject as will result in an accurate determination of pitch ihat 

 can be generally accepted. Alex.vnder J. Ellis 



Kensington, July 11 



P.S. — I have this morning received a letter from Herr 

 Appunp, in which he tells me that the letter of Prof. Helmholti, 



quoted by Herr Koenig, was received eleven or twelve years ago, 

 and that the error of Herr Appimn's pendulum there pointed out 

 was corrected more than ten years ago. He also refers me to 

 pp. 46-7 of Prof W. Preyer's tract " Ueber die Grenzen der 

 Tonwahmehmung," Jena, 1876, in which, by a calculation there 

 detailed. Prof Preyer shows that the absolute pitch of two of 

 Ilerr Koenig's forks, which should have been 128 and 256, were 

 129-1 and 258-2 ; and says that "the determination is as exact 

 as possible, so that the first decimal place can be fully trusted." 

 I made another fork to be 2584, and I know by comparison of 

 several specimens that Koenig's forks do not always agree within 

 more than -2 vibrations. A. J. E. 



July l6 



On a Fish-sheltering Medusa 



While collecting some three weeks since on the south shore 

 of Killary bay in Connemara, I observed that out of a number 

 of the common Aurelia aurita moving about in a rocky inlet 

 below me, one was invariably accompanied by a small fish, of 

 about an inch or an inch and a quarter in length, which had 

 established itself inside of the hemispherical disc. 



Occasionally the Medusa turned in its pulsations, so as to 

 bring the umbrella ui.dermost, when the fish would shoot hastily 

 out, but the Medusa had no sooner righted itself, than the fish 

 returned, and seizing its opportunity, swam in between the 

 marginal tentacles, and close up to the fringes of the actinostome, 

 remaining distinctly visible through the pellucid disc. 



I afterwards noticed several other Aurelia similarly attended, but 

 was not able, unfortunately, to identify the fish, which invariably 

 darted off at the most distant approach of a landing-net— it 

 appeared, however, so far as I could judge, to be the young ot 

 one of the larger species. Perhaps some of your readers could 

 contribute suggestions on that point. 



Associations of a similar character have, I know, been fre- 

 quently observed in the case of the Phjrsalid;:e and other 

 Acalephae, but not, so far as I am aware, in connection with this 

 species. E. L.'vwless 



The Earth and Moon 



I HAVE only now (July 12) noticed Prof Tail's remark respecting 

 a sentence, or rather half a sentence, which he quotes from an 

 article of mine in the Cornhill Magazine for June. It runs thus : 

 '•What mathematicians call the moving force exerted by the 

 earth on the moon is eighty-one times greater than the 

 corresponding force exerted by the moon on the earth" This 

 admits of an interpretation implying gross ignorance on my part 

 — ignorance, viz., of the fact that the moon pulls the earth just 

 as strongly as the earth pulls the mo«n It also admits of an 

 interpretation accordant with fact, for the moving force exerted 

 by the earth on each unit of mass in the moon is eighty-one 

 times greater than the corresponding force exerted by the 

 moon on each unit of mass in the earth. I do not think 

 anyone is likely to believe that I made the mistake imputed to 

 me by Prof Tail, in this instance, any more than that I made 

 an equally absurd blunder which he attributed to me in your 

 columns several months ago, or that he himself made the ludicrous 

 blunder attributed to him (in jest) by my humorous friend. Prof. 

 Nipher, of St. Louis. But as a mere matter of fact, I may point 

 out that the half-sentence quoted by him is completed by a half 

 sentence leaving no doubt as to my real meaning, and is 

 immediately preceded by the statement that "the moon pulls 

 the earth just as strongly as the earth pulls the moon." 



Lotdon, July 12 Richd. A. Proctor 



Blue and Yellow Crocuses 

 Referring to Mr. W. B. Tegetmeier's letter in Nature, 

 vol. xvi. p. 163, I can say that I once had a pony born and bred 

 on Dartmoor, which had never seen oats until it came into my 

 father's stable in the fourth year of its age, and it refused them. 

 We induced it to eat oats by mixing them with hay and gradually 

 reducing the quantity of hay until the oats predominated. 

 Peczance, July 10 Thos. Cornish 



Japanese Mirrors 

 More than eleven years ago, in February, 1866, I published 

 in The Reader (since extinct), a letter giving, I venture to think. 



