572 



NA TURE 



[April II, 1889 



This is followed by a description of a small new species of 

 Lepidodendron. 



In a second new species, named Lepidodendron intermedium, 

 an apparently early form of exogenous zone is shown to exist. 

 When describing, in his previous memoir. Part xi. (see Plate 49, 

 ¥\g. 11), the stem now Aesign?LXeA Lepidodendron fuliginosum, 

 he showed that, in it, we have an example of the most rudiment- 

 ary and least perfectly developed form of an exogenous xylem 

 yet seen amongst these Carboniferous Cryptogams. In this ex- 

 ample, but a few radiating laminae of vascular tissues make their 

 appearance in the innermost cortex. In the plant now described, 

 though these few laminse are represented by a continuous cylin- 

 drical zone of tracheids, and though the laminae are arranged in 

 radial order, they are still embedded in a mass of cellular tissue, 

 much in excess of what constitutes the medullary rays in the 

 higher types of Lepidodendroid organization. 



A fourth new species of Lepidodendron is described, under 

 the name Z. Spenceri, in young states of which no medulla is 

 visible, but, in its place, a number of vertically elongated cells 

 and imperfectly lignified scalariform tracheids are seen, inclosed 

 within an outer series of perfectly lignified tracheids. 



A fifth new species, Lepidodendron parvulum, is also de- 

 scribed ; after which the author points out the differences 

 between the mode of development of the cellular medulla of 

 these exogenous Cryptogams, and that of the representative 

 organ among the Dicotyledonous Exogens. Amongst the ordin- 

 ary Exogens, the growing tip of a stem or branch is a mere 

 aggregation of cells, which mass is soon separated into two 

 zones by the development within it of a ring of vascular bundles. 

 The cells inclosed within this ring become the medulla, and 

 those external to it constitute the cortex. Such a pith sub- 

 sequently undergoes but a very limited enlargement. In most 

 cases a time arrives when it grows less with age, and ultimately 

 disappears ; but in the Lepidodendra, though the tip of each 

 growing stem was, in the first instance, also a cellular mass, an 

 axial solid bundle of vessels was developed in the centre of the 

 new growth almost at its very commencement. But it was only 

 after this growth had made some progress, and the twig had 

 become clothed externally with numerous leaves, that the first 

 traces of a medulla began to appear in the centre of the bundle. 

 It is thus clear that the medulla of these Carboniferous Lycopods 

 is not genetically homologous with that of an ordinary exogenous 

 flowering plant. 



The axial vascular medullary bundle expanded into a hollow 

 cylinder under the internal pressure of the growing medulla, 

 which latter not only attained to considerable dimensions, but 

 was a persistent organ. The ring inclosing the medulla supplied 

 all the vascular bundles going to leaves and in part to branches. 

 The author demonstrates that the branches are supplied with such 

 bundles in two ways ; when the growing stem divides dichotom- 

 ously, which it does as amongst living Lycopods, the medullary 

 vascular cylinder splits into two equal halves. But, besides this 

 mode, the author shows that very frequently comparatively small 

 segments are cut completely out of the vascular cylinder, in 

 which a gap is thus left where the bark and the medulla meet. 

 The angular segment thus detached develops into a solid cylin- 

 drical bundle, in which, in time, a medulla forms as before. 

 The author is inclined to believe that all these latter forms of 

 bundles only supply short abortive lateral branches, which most 

 probably supported Lepidostrobous fruits. 



March 21. — " On the Velocity of Transmission through 

 Sea-water of Disturbances of Large Amplitude caused by Ex- 

 plosions." By Richard Threlfall, M.A., Professor of Physics, 

 and John Frederick Adair, M.A., Demonstrator of Physics, 

 University of Sydney. Communicated by Prof. T. J. Thomson, 

 F.R.S. 



This paper contains an account of a large number of experi- 

 ments made with the object of determining the velocity of waves 

 of compression caused by explosions under water. 



The method adopted depended on the use of a certain 

 " gauge " devised for the occasion, whereby the arrival of 

 the disturbance at a given point was transmitted to a 

 chronograph. 



The disturbances themselves were caused by submarine 

 explosions of dynamite and gun-cotton in quantities varying from 

 nine ounces to four pounds. 



The distance over which the velocity was measured was about 

 200 yards. 



The water was that of the Pacific Ocean in the harbour of 

 Port Jackson, New South Wales. 



The chronograph was of the falling pendulum description, and 

 fired the charge automatically. 



The absolute time was obtained by comparing the chronograph 

 tuning-fork with an astronomical clock. 



The distance was obtained in terms of the standard yard of 

 New South Wales by means of trigonometrical survey. The 

 chief results for the range quoted are as follows : — 



The chief portion of the paper is occupied in the description 

 of the details of the precautions taken to make the measurements 

 as accurate as possible. This involves some chronographic 

 improvements. An explanation of the large observed velocity is 

 attempted. 



"On an Effect of Light upon Magnetism." By Shelford 

 Bidwell, M.A., F.R.S. 



Several experimenters in the early part of the present century 

 tried to magnetize iron and steel by the action of light, ^ but I 

 do not know of any recent attempts in this direction, and of late 

 years the thing has been generally regarded as impossible. 

 Under ordinary circumstances there can be little doubt that this 

 is the case, but, if a certain condition is fulfilled, we might, I 

 think, expect to find some evidence of the action of radiation 

 upon the magnetism of iron. 



The condition is that the susceptibility of the bar AB to be 

 operated upon shall be greater (or less) for a magnetic force in 

 the direction AB than for an equal one in the direction BA. 

 This paper contains a short preliminary account of a series of 

 experiments which have been undertaken with iron bars having 

 this property. Much yet remains to be done, which will require 

 a considerable amount of time, and for which special apparatus 

 must be constructed. In the meantime, the results already 

 obtained appear to possess sufficient interest to justify their 

 publication. 



The method of preparing the bars is as follows. A piece of 

 soft iron rod, which may conveniently be 10 or 12 cm. long 

 and from o'5 to i cm. in diameter, is raised to a bright yellow 

 heat and slowly cooled. When cold, it is placed inside a 

 solenoid, through which is passed a battery current of sufficient 

 strength to produce a field of about 350 or 400 C.G. S. units. 

 The iron when removed from the coil is found to be permanently 

 magnetized, and its north pole is marked for the sake of dis- 

 tinction with red sealing-wax varnish. The bar is then supported 

 horizontally and in an east and west direction behind a small 

 reflecting magnetometer, and over it is slipped a coil, which is 

 shunted with a rheostat, the resistance of which can be 

 gradually increased from o to 26 ohms. The coil can be con- 

 nected by a key with a single battery cell, which is so arranged 

 as to produce a demagnetizing force inside the coil. The 

 resistance of the rheostat is slowly raised, so that more and more 

 current passes through the col, the battery key being alter- 

 nately lifted and depressed until the magnetometer indicates 

 that the iron bar as a whole is perfectly demagnetized. The 

 strength of the demagnetizing force required varies according to 

 circumstances : it is generally about one-thirtieth or one-twenty- 

 fifth of the original magnetizing force. 



After this treatment the iron rod does not differ, so far as 

 ordinary tests will show, from one which has never been sub- 

 mitted to magnetic influences. Nevertheless, as is well known, 

 it possesses certain properties which distinguish it from a piece 

 of really virgin iron. In the first place, the magnetization in- 

 duced by a force acting in such a direction as to make the 



' Chrystal, "Encyclopaedia Britannica, 

 fjllowing na;nes : Morlchini, Mrs. Somerv 



toI. XV. p. 274, mentions the 

 ;, Christie, Riess, and Moser. 



