TRANSACTIONS OP THE SECTIONS. 19 



Extract from a Letter addressed to Professor Phillips. 

 By the Rev. Professor Walker, 3T.A., F.R.S. 



"Wadham College, Oxford, 

 July 2, 1851. 



"My dear Sir, — You will probably have in Section A. some remarks on the pen- 

 dulum experiment of Foucault. It may be interesting to the Section to know that 

 we have tried it at Oxford, in the Radcliffe Library, and with most satisfactory re- 

 sults. We have observed one point in the motion which may be worth recording, 

 and I have not seen this noticed in other experiments ; and it is this, that whenever 

 the plane of vibration approaches the magnetic meridian, the apparent motion of the 

 plane is accelerated, while it is proportionally retarded as it approaches the line 

 which is at right angles to the magnetic meridian. We have observed these effects 

 for more than three weeks. The acceleration in approaching the magnetic meridian 

 is nearly one degree per hour. I had hoped to have been able to present these results 

 in an accurate form, but I have not had time. 



" Our pendulum was at first an iron ball with a pointer underneath, weighing nearly 

 12 pounds, and suspended by a piano wire ; the length from point of suspension to 

 bottom is as nearly as may be 80 feet 6 inches. The time of one vibration is a little 

 short of five seconds, more accurately 4 "96 seconds. As some thought the iron ball 

 more susceptible of magnetic influence, it was about ten days ago replaced by a lead 

 one of the same weight with a brass pointer. The results, however (as I did not 

 doubt), are just the same as with the iron one. 



" I may mention that the observed periodic time of rotation in our experiments does 



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not differ more than a few minutes from that given by the formula i , , ^.^ , 



•^ sme of latitude. 



In one instance it came within one minute of \h.eoxy- truth. 



" Believe me, my dear Sir, very faithfully yours, 



" Robert Walker." 

 Note. — The conclusions in this letter are drawn from first and somewhat inaccu- 

 rate observations. The Radcliffe Library is a public room and was visited by num- 

 bers during the progress of the experiments. It is intended, during the quiet and 

 leisure of the long vacation, to repeat the observations with more care, and to try also 

 a copper ball and a copper wire. 



Inquiries into some Physical Properties of the Solid and Liquid Constituent 

 Parts of Plants. By Professor E. Wartmann of Geneva. 



Plants are furnished with different membranes, many of which can be obtained 

 separately. Such are the epidermis of leaves, stems, fruits, &c. These membranes 

 seem to belong to two classes. The first consists of those which are composed of 

 round cells. The second comprises the cuticles in which the elongated cells prevail. 

 When viewed in a polarizing apparatus (such as that devised by Prof Norrenberg), 

 the latter depolarize light. The action is very striking with the epidermis of Eucomis 

 punctata, and a plate of rock crystal with two inverted rotations. A similar action is 

 found when a ray of polarized heat is transmitted through the membrane. If these 

 organs have been steeped for a considerable time in acids or water, they are not de- 

 prived of these properties. 



The double-refracting power of those tissues is easily perceived by looking through 

 them at a distant window. There are two positions at right angles in which one 

 set only of the cross-bars is seen. The horizontal bars appear when the longer side 

 of the cells is vertical, and vice versa. In intermediate positions, two faintly-coloured 

 images of each are sometimes visible. 



If such a thin membrane is interposed between the eye and the flame of a candle, 

 spectra of interference are produced on both sides of the flame, in a direction parallel 

 to the greater length of the cells. The appearance is like that which Fraunhofer has 

 discovered in the network. 



Such a structure in the outer coating of a great many plants may, perhaps, not 

 be without some connexion with the ever-changing direction of the plane of polariza- 

 tion of the atmospheric hght and heat derived from the sun. 



The liquid parts of vegetables are in electrical relations to each other, which may 



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