30 



NA TURE 



May II, 1876 



be adjusted upon e of the same constellation, so as to 

 make that perfectly round." 



These remarks have an essential bearing upon the in- 

 vestigation of elements. The components must have 

 been very close at both Herschel's epochs — if there be no 

 mistake in the register — and this is not at first sight 

 readily explained by the curve exhibiting the motion of 

 the smaller star from Struve's earliest micrometrical 

 measures in 1825 to the present date. 



Herschel further remarked in 1802 that the appearance 

 of the components was much like that of " a planet with 

 a large satellite, or small companion," and strongly sug- 

 gestive of " the idea of a connection between the two 

 bodies, especially as they are much insulated." 



The Rotation of Venus.— In a note upon the time 

 of rotation and position of the axis of Venus, which 

 recently appeared in this column, reference was inad- 

 vertently omitted to Flaugergues' observations at Viviers 

 in July, 1 796, which, according to a communication from 

 Valz to the Astronotnische Nachrichten (No. 278, vol. xi), 

 seemed to favour Bianchini's period, and placed the north 

 pole of Venus in longitude 321° 20', with an elevation of 

 16° 28'. Details of the observations are wanting, but 

 Valz states that Flaugergues observed with " une ancienne 

 lunette k deux verres de 18 pieds de long, amplifiant 105 

 fois qu'il ditfort bonne." He also employed one of 14 feet, 

 and a telescope said to be good, which Legentil brought 

 from India. Valz adds : "J'ai vu le dessein original de 

 la tache, elle etait grande et de forme trapezoide arrondie, 

 &c." 



Hussey's vigorous but prejudiced defence of the extra- 

 ordinary period of rotation assigned by Bianchini will be 

 found in Astronomische Nachrichten, No 248. 



Fritsch, of Quedlinburg, thought some observations of 

 his in April 1801 indicated a period of 23h. 22m. (^Berliner 

 AstronotnUches Jahrbuch, 1804, p. 213). 



SONG OF THE SCREW 



A moving form or rigid mass, 

 Under whate'er conditions. 



Along successive screws must pass 

 Between each two positions. 



It tzirns around and slides along — 



This is the burden of my song. 



Tht pitch of screw, if multiplied 



By angle of rotation. 

 Will give the distance it must glide 



In motion of translation. 

 Infinite pitch means pure translation, 

 And zero pitch means pure rotation. 



Two motions on two given screws. 

 With amplitudes at pleasure. 



Into a third screw-motion fuse ; 

 Whose amplitude we measure 



By parallelogram construction 



(A very obvious deduction). 



Its axis cuts the nodal line 



Which to both screws is normal, 



And generates a form divine, 



Whose name, in language formal, 



Is " surface-ruled of third degree." 



Cylindroid is the name for me. 



Rotation round a given line 



Is like a force along. 

 If to say couple you incline. 



You're clearly in the wrong ;— 

 Tis obvious, upon reflection, 

 A line is not a mere direction. 



So couples with translations too 



In all respects agree ; 

 And thus there centres in the screw 



A wondrous harmony 

 Of Kinematics and of Statics, — 

 The sweetest thing in mathematics. 



The forces on one given screw, 



With motion on a second. 

 In general some work will do. 



Whose magnitude is reckoned 

 By angle, force, and what we call 

 The coefficient virtual. 



Rotation now to force convert, 



And force into rotation ; 

 Unchanged the work, we can assert. 



In spite of transformation. 

 And if two screws no work can claim, 

 Reciprocal will be their name. 



Five numbers will a screw define, 



A screwing motion, six ; 

 For four will give the axial line. 



One more the pitch will fix ; 

 And hence we always can contrive 

 One screw reciprocal to five. 



Screws — two, three, four, or five, combined 



(No question here of sex). 

 Yield other screws which are confined 



Within one screw complex. 

 Thus we obtain the clearest notion 

 Of freedom and constraint of motion. 



In complex III. three several screws 



At every point you find, 

 Or if you one direction choose. 



One screw is to your mind ; 

 And complexes of order III. 

 Their own reciprocals may be. 



In IV., wherever you arrive. 



You find of screws a cone. 

 On every line in complex V. 



There is precisely one ; 

 At each point of this complex rich, 

 A plane of screws have given pitch. 



But time would fail me to discourse 



Of Order and Degree, 

 Of Impulse, Energy, and Force, 



And Reciprocity. 

 All these and more, for motions small, 

 Have been discussed by Dr. Ball. 



ON THE TELEPHONE, AN INSTRUMENT 

 FOR TRANSMITTING MUSICAL NOTES 

 BY MEANS OF ELECTRICITY 



IN/TR. ELISHA GRAY recently read a paper before 

 ^^^ an American Society explaining his apparatus for 

 transmitting musical notes by electricity. He showed 

 experimentally how, by means of a current of electricity 

 in a single wire, a number of notes could be reproduced 

 simultaneously at a great distance, and how by this 

 means also a number of telegraphic messages could be 

 transmitted at once along a wire and separately received 

 at the other end. One of Mr. Gray's apparatuses was 

 exhibited in London at the last soiree of ihe Society of 

 Telegraph Engineers by the president, Mr. Latimer 

 Clark. The principle of the apparatus is as follows : — 



A vibrating reed is caused to interrupt the electric 

 current entering the wire a certain number of times per 

 second and the current so interrupted at the sending end 

 sets a similar reed vibrating at the distant end. ■ <- 



