^4 



NATURE 



[November 22, 1894 



over plains, such as the Oder at Breslan, and the Marne at its 

 junction with the Seine, the water-temperature remains through- 

 out the year from one to three degrees Centigrade warmer than 

 t 1 ■ 



Herr E. Lecher, in the Wiener Bcrichle, gives an account 

 of an experiment he has performed to test whether when a 

 magnet turns about its magnetic axis the lines of force remain 

 at rest or turn with the magnet. A magnet is dividei by an 

 equatorialiplane into two parts, which can turn independently. 

 I'nder these circumstances it is possible, by means of suitable 

 contact brushes, to obtain from the two extremities of the 

 magnet an induced current of such a magnitude as cannot 

 be explained by the cutting of the rotating lines of force by the 

 extremely short brushes employed. These currents can be ex- 

 plained if we suppose, as did Faraday at one time, that a 

 rotating magnet cuts its own lines of force which remain fixed 

 in space. 



Mr. Carl B.\Rfs, in the current number of the American 

 journal <ij Science, describes a simple chronograph pendulum 

 which is likely to be very useful to those who have no break- 

 citcuit chronometer or seconds clock at their disposal. It is a 

 simple mechanism by which an ordinary seconds pendulum is 

 both kept in motion and made to record its oscillations on one 

 or more chronographs sharply. The heavy metallic bob of the 

 pendulum is electrically connected with the knife-edge, and its 

 top is surmounted by a soft iron armature, which is attracted 

 during part of the swing by an electromagnet, and thus kept 

 in motion. A longer and very much lighter pendulum, con- 

 sisting of a flat bobsu-pendeJ by two wires, is suspended by the 

 side of the first, and swings in the same plane, but with a 

 longer period. As the heavy pendulum approaches it, it 

 (ouches a platinum spring projecting from the other bob. makes 

 current for a moment, and works the chronograph, and at the 

 same lime sends the current through the electromagnet. The 

 contact is quite momentary, as the spring causes the wire 

 pendulum to be hurled off ballistically. On its return it is 

 brought to rest, without rebounding, by a stop, against which it 

 leans till the seconds pendulum returns. The bob of the light 

 peoduluoi is made up of two small square parallel plates, 

 between which the wires and the platinum strip are clutched by 

 a single central screw. A band of platinum foil is wrapped 

 round the heavy bob, in order to ensure reliable electric contact. 

 The chronographs and the electromagnet are connected in 

 parallel. The records show that the time of contact does not 

 reach o'l sec. It is desirable to use electromagnets of high 

 resistance to prevent exhausting the battery. 



Part 1. of vol. vii. of Cohn's Beilmge is taken up with a 

 long paper, by Dr. W. Rothert, on Heliotropism. He finds 

 that the heliotropic .stimulus received on one part may be trans- 

 mitted to another part of the same organ, or even to a diHerent 

 organ, and there give rise to heliotropic curvature. The trans- 

 mission can only take place in a basipetal direction, and its rate 

 i< always small : in favourable cases 2 cm. per hour. Contrary 

 (o Darwin's views, he believes that the whole region which 

 b capable of heliotropic curvature, is also heliotropically sensi- 

 tive, although this sensitiveness is often unequally dislributed 

 in the same region. In all cases of this unequal distribution, 

 it is a small region at the ap<x of the organ which is 

 distinguished by a greater sensitivenes', whilst the rest ex- 

 hibits this sensitiveness often in a far less degree. Further, 

 the author investigated the effects of cutting off the apex of the 

 cotyledon of seedlings of grasses, and found that this gives rise 

 to two independent phenomena : a diminution in the rate of 

 growth of the base, and a complete suspension of its heliotropic 

 and gcotropic sensitiveness. Both these effecls are, however, 

 only temporary. It was also unexpectedly found that these 

 effects aic not consequent on every injury done to the cotyledon, 



NO. 1308, VOL. 51] 



but that large cuts made either into the apex, or even two semi- 

 sections made below the apex from opposite sides of the org.nn, 

 and only 2 mm. apart, do not cause the diminution in the r-ite 

 of growth, nor the sTispension of heliotropic and geotropic 

 sensitiveness, but that this is only effected by the complete 

 section of the cotyledon. 



Messrs. \V. Wesley and Son's "Natural History and 

 Scientific Book Circular," No. 122, contains a full classified list 

 of important works on botany. 



The thirteenth monthly part of "The Royal Natural 

 History " ^ Frederick Warne and Co.), bein^ the first part of 

 the third volume of the work, has been published. 



The Royal College of Physicians, Edinburgh, has just issued 

 the fifth volume of Reports from their Laboratory, edited by 

 Drs. J. Batty Tuke and D. Noel Patou. The volume presents 

 the results of investigations carried out during the past two 

 years. 



The ninth number of the handy and useful Alembic Club 

 Refrinls (Edinburgh : W. F. Clay) is devoted to Davy's 

 papers on the property and nature of " muriatic acid " and 

 " oxymuriatic acid," published in the Philosophical Transac- 

 tion: between iSog and iSlS. Our readers need hardly he 

 reminded that though Gay-Lussac and Thenard were inclined 

 to believe in the elementary nature of the latter, it was Davy 

 who established the correctness of this view. This reprint of 

 the eight communications to the Royal Society, on his experi- 

 ments to demonstrate the elementary nature of chlorine, will be 

 valued by students of historical chemistry. 



We have received No. 6 of The Scientific Roll, conducted 

 by .\. Ramsay, and dealing with the baric condition of the 

 atmosphere. This publication is intended to be a summary of 

 what is known of this subject from the works of various writers, 

 so that anyone may make himself acquainted with what has 

 been written without obtaining and reading the original books, 

 some of which are now difficult of access. The present number 

 contains notes taken from Prof. Kimtz' Vorlesiingen uher 

 Meteorolc:;ie, published in 1S40, and translated into English by 

 Mr. C. V. Walker in 1S45. I:i addition to retaining the 

 original scales, the author reduces ail values to what he terms 

 the " baric unit," which is taken as equivalent to one million 

 pounds weight on the square mile. Thus one inch of mercury 

 at 60° F., and under the ordinary pressure of sea-level, corre- 

 sponds to 2000 such baric units, and a millimetre under the 

 same conditions to 7874 baric units. 



Prof. Lothar Meyer communicates to the Berichlc a 

 warning note concerning the dangerous nature of explosive mix- 

 tures of acetylene and oxygen. It is a well-known fact, fre- 

 quently demonstrated upon chemical lecture-tables, that 

 detonating mixtures of hydrogen and oxygen, or of marsh gas, 

 ethylene, or carbon monoxide and oxygen, may be ignited in an 

 open glass cylinder without danger provided the vessel is not 

 narrowed at the neck, which would be likely to cause undue 

 pressure. Prof. Meyer states that he has frequently performed 

 the experiment with the above gaseous mixtures, employing a 

 strong straight glass cylinder four centimetres wide and with 

 very thick base, without ever having experieiice<l an accident. 

 Upon performing the experiment recently, however, with a 

 mixture of acetylene and two and a half to three times its volume 

 of oxygen, igniting the gas by approaching the mouth of the 

 cylinder to a flame, the cylinder was blown to innumerable frag- 

 ments in his hand, happily and almost miraculously without 

 injuring him, although unprotected by a cloth, and the report 

 of the explosion «as so loud as to deafen for a time those in the 

 neighbourhood. It has long been known that acetylene ex- 

 plodes with oxygen in closed vessels with great violence, fre- 

 quently destroying an eudiometer, but this remarkable destruc- 



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