464 



NATURE 



\JMarch 17 i88i 



garding the ine;iu distances, mean paths, &c., of mole- 

 cules on rarefying gases. For the relations computed 

 depend on known mathematical principles. The only 

 possible ground for question would be the particular data 

 of mean distance, &c., tal:en as a basis for the calcula- 

 tions. But it should be noticed that these rest on an 

 experimental basis : having been deduced from obseri'ed 

 facts by investigators of admitted competence, and by 

 means of several diverse lines of argument which are 

 found to accord in a remarkable manner as to the results, — 

 which is therefore strong confirming evidence of their 

 substantial accuracy. Also the above inferences regarding 

 a mechanism for the fundamental purposes of carr>ing 

 energy, storing energy in equilibrium, and producing 

 effects of approach (such as gravity, cic), cannot as me- 

 chanical facts admit of any question. For mechanical 

 principles (like mathematical truths) hold independently 

 of any inquiry as to whether they actually find practical 

 application in nature or not. The best argument for their 

 practical application in nature is the incomprehensibility 

 of observed facts without them. We can at least say with 

 certainty that under such conditions, effects (phenomena of 

 approach,' transferences of motion, &c.) of the character 

 observed would be produced,— and which effects have not 

 hitherto found any explanation that appeals to our reason. 

 The certainty of simple and automatic mechanical con- 

 ditions being conceivable which are capable of producing 

 such important effects, should lend a legitimate interest 

 to these inquiries, and the mechanical beauty of the 

 "radiant" adjustment of moving particles of matter 

 which adapts them to so many noteworthy purposes at 

 once, should surely itself be an argument in favour of the 

 practical application of the scheme in nature,— as a simple 

 means to great and important ends. 



S. ToLVER Preston 



DEEP-SEA OPHIURANS 

 T N the anniversary Memoirs ai the Boston Society of 

 Natural History, Prof. Theodore Lyman gives an 

 account of a structural feature hitherto unknown among 

 Echinodermata which he has discovered in deep-sea 

 Ophiurans. The remarkable structures described ap- 

 pear under the microscope as little tufts resembling 

 bunches of simple Hydroids on the sides of the arms 

 of certain Ophiurans. On careful examination these tufts 

 are foutid to be bunches of minute spines, each inclosed 

 in a thick skin-bag, and in form resembling agarics, or 

 parasols with small shades. They are arranged in two 

 or even three parallel vertical rows, and in this respect 

 the animals on which they occur differ from all other 

 Ophiuridae known, lor all others possess a single row 

 only of articulated spines. The peculiar tufts, which 

 are apparently homologous with pedicellaris, are at- 

 tached to the outer joints of the arms, near the margins 

 of the side arm- plates. Two new genera, Ophiotholia and 

 Ophiobelu^;, closely allied to Ophiomyces, are described in 

 which these curious appendages occur. The species of the 

 gene'-a are soft with imperfect calcification. E,\amples of 



' It would n^t be difficult substantially to imitate what occursin gravitation 

 taccordmg to the dynamical tlieory). by ccol.ng down the opposed faces of 

 two metal disks freely suspended in a moderately large vessel of rarefied gas 

 at a less distance apart than the mean length of path of the gaseous particles.— 

 When from known principles (already experimented on by Mr. Crookes) the 

 two disks would approach. Here the diminished velocity of rebound of the 

 gaseous particles fr _m the cooled inner surfaces of the disks (which entails 

 tne appr.ach), is imitated m gravitation by a similar diminished velocity of 

 reDound ot the gravific particles from gross matter, owing to their translatory 

 moti. n being partly shivered into vibration (and rotation) at the shock of 

 SP-f ,w^'"°«/'■°'^■"^"'^A(■" * manner elucidated by §ir W. Thomson, 

 Fliil. Mag., May, 1873). On a largescale, a similar diminution of translatory 

 motion at impact is universally illustrated by the known retarded rebound 

 of cla-lic masses at colhsion.-wben part of the translatory motion is (in a 

 somewhat analogous way) converted into a vibratory cr rotatory motion . f 

 nln,, , f t""*'' "' """ "I"" """=■■■ I' becomes interesting in a dynamical phe- 

 nomenon of the nature of gravitation to contemplate the possibility of diing 

 something towarc-s illustrating it experimentally, and to acquire the certainty , f 

 th« existence of the streams cf particles which produce ihe efrect,-by almost 

 visualising them, through the means employed in the recent researches by 



Ophiotholia were dredged off Juan FernandcE, in 1825 

 fathoms, and of Ophiohelus off'Barbadoes in 82 fathom:^, 

 and off Fiji in 1350 fathoins. 



Prof. Lyman states that among the Ophiuridse and 

 Astrophytidae of the Challenger Expedition the entire 

 number of new genera brought home is 20 ; that of 

 species 167. 



AN ELECTRICAL THERMOMETER FOR 

 DETERMINING TEMPERATURES AT A 

 DISTANCE 



'T'HE success of many industrial operations depends 

 -*■ upon the steady maintenance or proper variation of 



certain temperatures, and it is often of the highest 



importance that the person in charge of these operations 



should be able readily to ascertain by means of the 



thermometer if the workmen are performing their duties 



correctly. It sometimes happens 



that thermometers have to be placed 



in positions which are difficult of 



access, or removed some distance 



from the centre of the manufactorj', 



and that considerable time has to 



be expended in visiting the different 



stations. It was in order to meet 



the requirements of such a case as 



this that the electro-thermometric 



apparatus here described was con- 

 structed. 



I had for some time been much 



in need of an instrument whicli 



would admit of the temperature of ,1 



series of malt-drying kilns bcin 



determined at a considerable di 



tance from the kilns theinselvc 



and, not being able to meet with .i 



description of a suitable instrumen 



I was led, after several trial?, 1 



contrive this apparatus, which, .il 



though it does not embody any ne\i 



principle, and is not perhaps adaptci I 



to accurate meteorological work, 1^ 



nevertheless very suitable for tl;(_ 



technical purpose for which it wa^ 



originally designed, and is doubtlebi 



capable of extended application in 

 many industries. 



The apparatus consists essential!) 

 of two parts, a mercurial electro- 

 thermometer, and a combination of 

 apparatus which constitutes an au- 

 tomatic receiver and transmitter of 

 signals from the thermometer. 



The thermometer, which is shown 

 in Fig. I, was constructed for me bv 

 Mr. J. Hicks of Hatton Garden. A 

 is an ordinary thermometer abou' 

 nine inches in height, with a lar^,^ 

 bulb and a stem of wide bore. 

 Through the side of the stem, and 

 fused into the glass, are inserted a 

 series of short platinum wires, the 

 free end of each being connectetl 

 with a binding screw. These wires, 

 which project slightly into the bore 

 of the thermometer, are, in my " 



instrument, inserted at intervals of 3° F. between 120' 

 and 171', the range of temperature required in this 

 case. The constructor of this part of the apparatus 

 informs me that, if necessary, there is no practical diffi- 

 culty in inserting wires at intervals of a single degree, or 

 even less, without interfering with the calibration of the 

 tube. The upper part of the bore of the tube is expanded 



