684 



being by no means steady and uniform, but subject to alternating 

 changes of greater or less amount. The effects exhibited on these 

 wires, and which, from the experiments, were found to occur on the 

 north of Derby as well as on the south, would be accounted for by 

 supposing that they were caused by alternating currents of elec- 

 tricity on the earth's surface in a northerly and southerly direc- 

 tion, proceeding towards the north until 9 a.m., and towards the 

 south until from 7 to 12 p.m., and then again turning northwards; 

 agreeing, therefore, nearly in point of time with the usual times gf 

 daily change in the direction of the magnetic needle. The experi- 

 ments, as has been stated, were continued during a fortnight, and 

 the deflection noted every five minutes, day and night. The 

 paper contains the tabular records of these observations ; and also 

 diagrams are given exhibiting the daily path of the needle. 



The author concludes his paper by expressing his regret that his 

 avocations do not allow him sufficient leisure to prosecute this in- 

 quiry, but that he will be happy to place in the hands of any person 

 desirous of pursuing the subject all the tables and results which he 

 has collected. 



5. " On the Direction assumed by Plants during their growth." By 

 Professor Macaire, of Geneva. Communicated by P. M. Roget, 

 M.D., Sec. R.S., &c. 



This paper is divided into three sections. 



The first section contains an account of some observations and 

 experiments made by the author on the phenomena of the curling 

 of the tendrils of the Tamus communis. After a description of the 

 tendril, w^hich in this plant is the footstalk of an abortive leaf, the 

 author shows that the contractile power of the organ is excited by 

 contact with any object whatsoever, and even with another part of 

 the same plant ; that the curling begins at the point of contact, but 

 continues in both ends of the tendril, either forming knots, if there 

 be something to embrace, or taking the shape of a cork-screw, if 

 there be not. The knots are completed in a few minutes, and exert 

 a considerable degree of pressure. A separation from the plant 

 stops the curling up of the tendril. The curling always takes place 

 in the same direction from the outside inwards. When the tendril 

 is immersed in water, or in a solution of gum, it does not contract ; 

 but at the same time it does not lose the faculty of curling up by 

 contact with a solid body. Ammonia, alcohol, or Eau de Cologne 

 have little or no effect. Diluted sulphuric and nitric acids, even 

 the vapours alone of the last, without actual contact, immediately 

 excite in the tendril an energetic contraction. The same thing 

 happens with a solution of corrosive sublimate. On the contrarj^, 

 prussic acid stops the curling up that had already begun, and renders 

 the tendril incapable of being again excited by the contact of a 

 solid body. 



The conclusions which the author comes to on this subject are, 

 that the contractions of tendrils cannot be explained by the hypo- 

 theses of Knight and De Candolle of an unequal action of light on 



