472 



NATURE 



[April i^, 1875 



indicates and measures with great exactitude the various 

 increases in the power or strength of the received electi-ic 

 current, the motion of the spot of light following every 

 variation of the current, thus affording a record to the 

 eye of the value of the current under circumstances and 

 conditions in which ordinary instruinents indicating the 

 liiere presence or absence of a given strength of current 

 would be valueless. 



In the Syphon Recorder about to be brought under 

 notice, the same remarkable feature of presenting the 

 ever-varying value of the received current at the end of 



the cable, or the strength of the cvirrehi, is preserved, 

 while at the same time a pei-manent automatic record is 

 registered for reference. 



The difficulty to be overcome in the construction of such 

 a recording instrument has been chiefly that due to the 

 mechanical problem of obtaining marks from a very light 

 body in rapid motion without impeding or interfering 

 with that motion. The combination of parts and prin- 

 ciples employed in the syphon recorder will be found to 

 be more or less previously well known ; the merit of Sir 

 William Thomson's beautiful instrument consists in that 



Fig. 17.— SIi 



I Thomson's "mirror " or reflecting galvanometer. 



he has combined well-known forms and principles to- 

 gether in such an arrangement and combination of parts 

 as to produce new and useful results. It is combinations 

 such as those now to be described that constitute the 

 value of scientific research in relation to mechanical 

 applications. 



It should be remembered that it is not possible to 

 patent a principle, but only the application of a principle. 

 If this axiom were more frequently remembered, the 

 severe strictures upon patents in general that have already 



been made in these articles woiild have been rendered 

 unnecessary. The "syphon recording" instrument fitly 

 illustrates in what a good and valuable patent consists. 

 With old and well-known parts and principles such as 

 permanent-magnets, electro- magnets, coils, armatures, 

 syphons, capillary attraction, and hydrostatic pressure 

 and such like material, novel and practical results have 

 been produced. 



[To be continued.) 



OUR ASTROKOMICAL COLUMN 

 The Solar Eclipse of 1900, May 28.— We refer to 

 this eclipse with the view of correcting an error in Hal- 

 laschka's " Elcmenta Eclipsium," where it is stated to be 

 annular. It is really the last total eclipse visible in 

 Europe during the present century. The following ele- 

 ments may be expected to be pretty near the true 

 ones : — 



Corjuncticn in R.A. May 28, at 2h. 56m. 22s. c.M.T. 



P. A 



Moon's hourly motion in R.A. 

 Sun's ,, ,, 



Moon's declination 



Sun's ^„ ,, 



64 56 49 



37 17 



2 32 



21 50 17 N. 



21 27 15 N. 



Moon's hourly motion in Deck 



Sun's „ ,, 



Moon's horizontal parallax 



Sun's „ ,, 



Moon's true semidiameter 



Sun's 



The sidereal time at Greenwich mean noon, is 

 4h. 22m. i6sS, and the equation of time 2m. 59s. additive 

 to mean time. 



The central eclipse enters Europe noarOvar, on the coast 

 of Portugal, and passes off Spain a little south of Alicante. 

 In longitude oh. 34m. os. W. and latitude 40^49' N. on 

 the Portuguese coast, totality commences at3h. 27m. local 

 mean time, and continues im. 30s., the sun at an altitude 

 of about 43°. At AHcante it commences at 4h. lom. iis. 



