Nov. 26, 1 885 J 



NA TURE 



lage in respect to the points raised here with the figure of the 

 external anatomy of the adult on plate 73 in my " Sketch of 

 the Life- History of the Oyster," already cited. 



Mr. Cunningham's inference that the left valve, usually 

 regarded as the lower one, is really the upper, because he finds 

 worm-tubes and hydroids most abundant on the convex or left 

 valve, is founded upon an imperfect acquaintance with the habits 

 of the oyster. For, if living oysters are thrown into the water 

 they will invariably fall upon the bottom with the left valve down- 

 ward. If dead oyster-shells — free valves — be similarly thrown 

 into the water, they will invariably fall with the hollow side up, 

 and the convex one down. And furthermore, both living and dead 

 shells remain in just the position in which they fall. Dead 

 shells sown as cultch, or collectors, fall in such a position, and 

 most of the spat is "caught'' on the exposed parts of the under 

 surface of such shells, whereas little is found on the upper 

 surface. The reason for this is that the sediment which is 

 deposited on the upper surfaces, asphy.xiates the young oyster- 

 fry and the other larvte which affix themselves before they can 

 become established and strong enough to resist its effects. The 

 affixed organisms on the exposed inclined under surfaces of the 

 shells, are, on the other hand, protected from the accumulation 

 of sediment. 



It is also well known that the right valve of the oyster is 

 always the most deeply pigmented, while the lower or left one 

 is paler. This is always the case when oysters lie almost flat on 

 the bottom. When crowded together on the natural banks in a 

 vertical position, there is less difference between the colours of 

 the valves. This difference is obviously due to some influence 

 exerted by the position of the aspects of the body of the animal 

 in respect to light, the same as in land and aquatic animals 

 generally. I would conclude, for this last reason alone, that the 

 right valve of the oyster is normally always uppermost, were it 

 not for the fact that I have observed all the stages of transition 

 from the spat to the adult condition in confirmation of such a 

 conclusion. It is true that many young oysters have the right 

 valve looking down when allowed to grow upon cultch or shells 

 which have been sown upon the bottom to favour the collection 

 of the spat, but that circumstance by no means subverts the 

 conclusions of such cautious and careful observers as Brooks, 

 Woodward, Jeffrey, Huxley, Horst, and others. 



John A. Ryder 



Smithsonian Institution, Washington, U.S.A., 

 November 1 1 



The Rotation Period of Mars 



One or two points in Prof. Bakhuysen's investigation of the 

 .rotation period of Mars require correction : — 



First, my determination of the period, as finally corrected, 

 |was 24h. 37m. 22725., correct within 002s. The correction 

 arose from the detection of a small clerical error. My final 

 result was deduced from a comparison of observations by myself 

 in 1873, with observations by Kaiser in 1864, Madler in 1830- 

 1837, Sir W. Herschel in the last quarter of the eighteenth cen- 

 tury, Huyghens and Hooke in 1666. I have since used the 

 •best observations during the oppositions of 1S81 and 1S83, with- 

 out finding any occasion for changing my result even by one- 

 j hundredth part of a second, though I place no reliance on the 

 ' second decimal figure. 



But, secondly. Prof. Bakhuysen, like Mr. Denning some time 

 'since, has taken Kaiser's result uncorrected for the clerical 

 errors — very seriously affecting it — which I detected in 1873. 

 Kaiser counted three days too many in comparing Hooke's ob- 

 j servation with his own : one day through a mistake in cor- 

 irecting for change of style, and two days (apparently) from 

 ! counting the years 1700 and 1800 as leap-years. His thus 

 taking three days too many of terrestrial time had the effect — 

 I since three corresponding Martian rotations were taken in — of 

 I introducing a deficiency amounting to three times the excess of 

 a Martian over a terrestrial day, that is, 3 X 37m. 227s., or 

 67,281 tenths of a second. This, divided by the total number of 

 Martian rotations, about 88,900, gives as a correction about 

 o'077s. to be added to both Kaiser's estimates, making them 

 I respectively 24h. 37m. 22'697s. and 24h. 37m. 22'668s., the 

 jmean of which, 24h. 37m. 22'6S25s., is practically the same as 

 the value I assigned, viz. 24h. 37m. 227s. 



I think it probable that Schmidt (and perhaps Prof. Bakhuy- 

 sen, too) followed Kaiser so far as the error of three days was 



1 



concerned. It would naturally be taken for granted that this 

 part of Kaiser's work was free from error. If I had not been 

 determined to find out where and how Kaiser's calculations 

 differed from my own, I should not have found out his mistake, 

 for certainly one would not expect to find two large errors in a 

 work perfectly free from small ones. But so it was. I may 

 remark that Prof. Newcomb, of Washington, went through my 

 calculation, finding it correct, and that Kaiser really had made 

 the mistake I indicated. 



As this correction re-established what Kaiser had doubted, 

 the accuracy of Hooke's observations, and of my own interpre- 

 tation of them. Prof. Bakhuysen's correction is scarcely ad- 

 missible. For a difference of o"o6s., multiplied by 88,900 for 

 the Martian rotations between Hooke .and Kaiser in 1873, gives 

 a total discrepancy of an hour and a half, nearly all of which 

 must be assigned to Hooke's observations and Huyghens' 

 (which I brought into agreement with Hooke's by correcting 

 Kaiser's one-day error for change of style). 



RicHD. A. Proctor 



5, Montague Street, Russell Square, W.C., November 23 



Beloit College Observatory 



My attention has been called to a paragraph in Nature 

 (vol. xxxii. p. 514), which, quoting from Science, speaks of 

 "the Astronomical Observatory of Beloit College as closed for 

 lack of funds. " 1 1 is not strange that you express surprise at 

 this announcement. Permit me to say that it is positively 

 untrue. So far as I can learn, the only authority for it is a 

 strange and entirely unwarranted statement from our late 

 Director. Mr. Tatlock's connection with our Observatory 

 closed on July t last. Within one week of that date Mr. Charles 

 A. Bacon was appointed his successor, and a few weeks later 

 he appeared and took charge. He has already proved himself 

 competent, both as an observer and as an instructor. New 

 arrangements are made for both meteorological and astro- 

 nomical observations, and special attention will be given to 

 solar and spectroscopic work. Though not richly endowed, 

 our "Smith Observatory" is well equipped, and under its 

 present direction its facilities will be made helpful to both the 

 advancement and the diffusion of science. A. L. Chapin 



Beloit College, Wisconsin, October 31 



CONFERENCE OF DELEGATES OF CORRE- 

 SPONDING SOCIETIES OF THE BRITISH 

 ASSOCIATION, HELD AT ABERDEEN 



A NEW branch of the British Association glided un- 

 **- obtrusively into e.\istence at Aberdeen, under the 

 new rules passed in the previous year : I mean the Con- 

 ference of Delegates of Corresponding Societies. The 

 Committee to whom the general arrangements connected 

 with this new branch is intrtisted are now issuing a 

 circular to the Corresponding Societies, signed by myself 

 as its Chairman, and by Prof. Meldola as its Secretary, 

 in which they give an account of the proceedings at 

 Aberdeen, with comments thereon. Much of this will be 

 of general interest, as it helps to explain the functions 

 of the Conference, which, as the proceedings showed, 

 were imperfectly understood by many of the delegates 

 themselves. The report is too long to ask you to print it 

 in full, and on the other hand its general purport is more 

 easily seized by leaving out details. I therefore limit 

 myself to sending you extracts from it, with connecting- 

 links of e.\planation to make them read continuously. 



The Corresponding Societies Committee of the British 

 Association beg to lay the following statement of work done at 

 Aberdeen, with comments thereon, before the Presidents and 

 Councils of the various Societies whose applications for enrol- 

 ment as Corresponding Societies of the British Association had 

 been granted. 



The Conference of Delegates was held on Thursday, Sep- 

 tember 10, and on Tuesday, September 15, both meetings 

 having been called at 3.15 p.m., and lasting in each case about 

 one hour. 



