December 7, 1893] 



NATURE 



141 



of the kinds named were grown from the seeds in the various 

 tubes. But in no one instance was there the smallest deviation 

 in any respect from the standard type grown from the corre- 

 sponding control packet. 



In the case of the beet-root, a larger number of plants were 

 developed in many of the pots than the ten seeds which had been 

 sown in each. This I found to be due to the fact that beet-root 

 seeds very frequently throw up two seedlings apiece. Not so 

 frequently, but still very often, they yield three, and sometimes 

 even four. 



Further experiments are in progress. 



" On hepatic glycogenesis," by Dr. Noel Paton, Superinten- 

 dent, Research Laboratory of the Royal College of Physicians 

 of Edinburgh. 



The object of the research is to determine the mode of con- 

 version of glycogen to sugar in the liver. Is it due to a zymin, 

 or to the metabolism of the liver protoplasm ? A study of the rate 

 of conversion of glycogen in the excised liver at the body 

 temperature shows that there is an initial rapid and a subsequent 

 slow stage in the process. The former occurs before visible 

 morphological changes can be detected in the cells ; the latter 

 goes on after the cells are disorganised. The former is inhibited 

 by destroying the cells (by pounding with sand), and by the 

 presence of one per cent, of fluoride of sodium ; the latter is 

 not stopped thereby. The product of the former is glucose ; of 

 the latter, glucose with dextrin and, possibly, maltose. Agents, 

 such as chloroform, ether, and pyrogallic acid, hasten the 

 disintegrative changes in the cells, and accelerate the early 

 rapid stage of conversion, but do not influence the later slower 

 stage. During life the firsi may produce glyceemia by this 

 action on glycogen conversion. They seem to act by hastening 

 the katabolic changes immediately preceding cellular death. 

 Drugs, such as curare, morphin, and nitrite of amyl, which 

 cause glycsemia, do not do so by increasing the conversion 

 of glycogen ; they do not accelerate the morphological changes 

 in the cells. These observations show that the early rapid 

 changes are due to the metabolism of the protoplasm. The later 

 slower changes are not due to the acid which develops, nor are 

 they, to any marked extent, due to the action of micro-orga^iism ; 

 they seem to be brought about by a zymin developed as a result 

 of the disintegration of the cells. 



November 23. — "Magnetic Observations in Senegambia." 

 By T. E. Thorpe, F.R.S., and P. L. Gray. 



On the occasion of the recent Eclipse Expedition to Se »e- 

 gambia we took with us a set of magnetic instruments of the 

 Kew pattern, with a view of making observations in a district 

 for which the magne ic elements have not hitherto been deter- 

 mined. 



Observationsweremadeat Fundium, Senegal, and atBathurst, 

 on the River Gambia. 



The results are as follows :— 

 Fundium, Senegal, lat. 14° 7'"4 N., long. 16° 32' W. (approx.). 



The observations were made on April 4, 5, and 14, 1893, in 

 the vicinity of the Eclipse Camp and on a partially enclosed 

 piece of ground between the Administrator's house and the River 

 Salum, about 80 yards from the shore. The temperature during 

 the force observations was about 30° C. 



The results are as follows : — 



Declination ... ... = 18° 44' W. 



Horizontal force ... ... = o '30409 c.g.s. 



Dip = Needle i, 29° 9''i 



= ., 2, 29''8'-2 



Bathurst, River Gambia, lat. 13° 28' N., long. 16° 37' W. 

 The station was on a large piece of open ground and near the 

 centre of McCarthy Square. All the observations taken were 

 made on April 20, 1893. 



Declination ... ... = 18" 50' W. 



Horizontal force ... ... = 0*30514 c.g.s. 



Dip = Needle I, 28° 43'-4. 



,, ... ... ... = ,, 2, 28° 42'"I. 



Physical Society, November 24. — Prof. A. W. Riicker, 

 F.R. S., President, in the chair. — Colonel Maitland, C.B., 

 was elected a member of the Society. Prof. S. P. Thomp- 

 son then occupied the chair whilst the President read a 

 paper on the magnetic shielding of concentric spherical 

 shells. In this mathematical investigation the author considers 

 cases in which the equipotential surfaces are surfaces of revolu- 

 tion about a line through the centre of the shells, and the per- 



NO. T258, VOL. 49] 



meability (/u) of each shell is constant. Taking the common 

 centre as origin, the potential within any shell is expanded in 

 terms of zonal spherical harmonics, and the ratio of the shielded 

 to the unshielded field determined. The following important 

 result is arrived at, viz. if the permeabilities of the enclosed and 

 external space be the same, then the ratios of the shielded to the 

 unshielded fields are the %'i.'me. for each harmonic term, whether 

 the part shielded be external or internal. It is also shown that 

 the shielding effect on external space when a small magnet is 

 placed at the centre of the shell is the same as the shielding 

 effect on the enclosed space when the shells are placed in a 

 uniform magnetic field. The case of a single shell with a small 

 magnet at the centre is next considered where the permeabili- 

 ties of the internal and external spaces are taken as unity. 

 Here the shielding depends on the ratio of the outer to the inner 

 radius (flj/afl). When the thickness of the shell is i/ioo of a^ 

 the ratio of shielded to unshielded field (^/i^,,) 's 3/13 when 

 fji = 500, and 3/23 when yu = 1000. For fi = 1000, in- 

 creasing the thickness from a i/io to a 1/2 changes the shielding 

 from 1/60 to 1/194, thus showing that after the shell is 

 moderately thick, further increasing the thickness is not very 

 effective. When the small magnet is displaced from the centre 

 of the shell with its axis along a radius, then the shielding effect 

 of the shell is greater on the side towards which the magnet is 

 moved, and less on the opposite side. Thickening a single 

 shell being inefficient, the effect of using two or three shells separ- 

 ated by air-gaps is investigated. Here, as in the case of a single 

 shell, the shielding is improved by adding permeable material 

 either within the inner or without the outer shell. If the inner 

 and outer diameters are given then when the difference in these 

 diameters is small, one continuous shell gives the best result. 

 For a larger difference, two shells separated by an air-gap are 

 much more efficient than a single one, and filling up the air-gap 

 would appreciably diminish the screening effect. When the 

 permeability of the substance is high the best shielding is 

 obtained when the radii of the bounding surfaces of the shells 

 are in geometrical progression. The great value of lamination 

 is shown in the following table, where the volume of the per- 

 meable material is expressed in terms of that of the enclose*' 

 space, and the shielding in each case being the best. 



The conditions for the best arrangement in each of the 

 following cases are fully worked out in the paper, viz. 

 Two shells when the largest and smallest radii and the 

 volume of the material used are given ; two contiguous shells 

 of different permeablities ; and three shells of different perme- 

 abilities. The main results of the investigation are that with 

 thin shells lamination is useless, while with thick shells it is 

 essential, if the best effect is desired. Experiments made on 

 actual shells had fully confirmed the theoretical conclusions. 

 Prof. Minchin said the mathematical results were very simply 

 expressed. Although the work was apparently restricted to 

 zonal spherical harmonics, some of the important formulae apply 

 equally to general spherical harmonics. Referring to the diffi- 

 culty of shielding by single thick shells, he pointed out that the 

 equation giving the relation between the shielded and unshielded 

 fields with different thicknesses of shell represented a hyperbola 

 with its asymptotes parallel to the axes ; hence the shielding 

 tended to a definite limit as the thickness increased indefinitely. 

 Mr. Evershed said he had been engaged for the last two years 

 on the subject of magnetic shielding, with a view to screening 

 measuring instruments from external fields. In such cases it 

 was not possible to use closed shells, and this introduced 

 trouble. The best results he had yet obtained was to reduce the 

 disturbance to about one-fifth. Another difficulty was intro- 

 duced by the fact of the shields being magnetised by the cur- 

 rent passing through the coil, and owing to hysteresis, the per- 

 meability was different according as the magnetisation increased 

 or decreased. By using an outer iron shell a great improve- 

 ment had been effected. To obtain the best results, it was 

 important to have no joints in the shields. A coil 

 fiame with two shields of bent iron was exhibited. 

 Mr. J. Swinburne remarked that the subject divided itself into 

 two, shielding of instruments and shielding sources. If a 



