.l7l^. 19, 1875J 



NATURE 



317 



such a cylinder can be pressed through openings of 

 smaller diameter, &c. It was thus shown that under a 

 strong pressure ice can be formed into any desired 

 shape, that it behaves plastically even on a small scale, 

 in the same way as the gigantic ice-rivers of glaciers do 

 on a large one, adapting themselves to the narrower or 

 wider parts of the valleys through which they flow. The 

 phenomenon discovered by Faraday in the year 1850, 

 which was afterwards widely discussed, and which was 

 called regelation, formed the key for the explanation of 

 this behaviour. Not one, however, of the men of science 

 mentioned has tried to determine the exact pressure 

 under which ice changes its form ; all of them have 

 worked with very high pressure, which in fact is neces- 

 sary to obtain results that are visible in a short time. 

 Only Moscley has made several series of experiments, 

 to ascertain at what pressure or draught ice tears, is 

 crushed, or when its plasticity becomes perceptible, i.e. at 

 what pressure a dislocation of the ice-particles takes 

 place. He found, that to tear an ice-cylinder apart, 

 for each square inch of its base a weight of from 70 to 

 116 lbs. was necessary according to the higher or lower 

 temperature (representing a pressure of 5^ to 9 atmo- 

 spheres). To break an ice cylinder by pressure, ioi*8 lbs. 

 were necessary for each square inch ; and to cause a dis- 

 location of the ice-particles, from 97*89 lbs. to 118 lbs. 

 were required [y^ to 9 atmospheres). 



Herr Pfaff, of Erlangen, has lately made a series of 

 experiments in order to obtain some more exact nume- 

 rical values for the degrees of pressure which change 

 the form of ice to any apparent extent ; it is particularly 

 interesting to know with reference to the glacier motion, 

 what is the minhmun of pressure at which ice still 

 remains plastic, i.e. yields to pressure. It was found 

 that even the smallest pressure was sufficient to dis- 

 locate ice-particles tf it acted continuously, and if the 

 temperature of the ice and its surroundings was near 

 the melting-point. At a pressure of two atmospheres ice 

 showed itself so yielding, that for instance a hollow iron 

 cylinder of irs mm. diameter and 17 mm. thickness of 

 side entered 3 mm. deep into the ice within two hours, 

 and at a temperature of between - 1° and +o"5°. The 

 following will show the influence of temperature. The 

 same iron cylinder under the same pressure entered 

 I '25 mm. deep into the ice in twelve hours at a tempera- 

 ture of between - 1° and - 4° ; while at a temperature 

 varying between - 6° and - 12° it only entered i mm. 

 deep in five days, at a pressure of five atmospheres, or 

 only o"i mm, in twelve hours. If the temperature of the 

 surroundings rises beyond the melting-point the ice be- 

 comes so soft that in one hour the same iron cylinder 

 under the same low pressure entered 3 cm. deep into the 

 ice, although it was completely surrounded by snow in 

 order to prevent the temperature of the cylinder itself 

 rising beyond 0°. In all these experiments a one-armed 

 lever was used to regulate the pressure ; it consisted of a 

 steel rod of 86 cm. length, which had a boring at its 

 end and was fastened to a steel plug round which it 

 could easily be turned. By this simple contrivance any 

 desired pressure could be maintained for any length of 

 time. These and other experiments (which were made with 

 a pressure of only I atmosphere) show that the plasticity 

 of ice at a temperature near its melting-point is very 

 great even at the lowest degrees of pressure. Herr Pfaff 

 is of opinion that at this temperature the plasticity of 

 the ice only becomes nil when the pressure itself is nil, 

 but that it decreases very quickly as the temperature gets 

 lower. 



The opinion is still widely spread, based upon some 

 experiments of Tyndall, that ice is not in the least 

 flexible or ductile, although lately several observations 

 have been made which force us to ascribe some flexibility 

 to that substance. Kane observed, for instance, that a 

 large slab of ice resting with its edges on two other 



blocks, bent itself under its own weight after a lapse of 

 several months. Herr Pfaff experimented with a paralklo- 

 piped of ice of 52 cm. length, 2*5 cm. breadth, and 1*3 cm. 

 thickness. It was placed with its two ends on wooden 

 supports, so that on each side 5 mm. were resting on 

 wood. From Feb. 8th to Feb. 15th, when the tempera- 

 ture remained between — 12° and — 3*5°, the middle 

 sunk very little, on the average 2 or 3 mm. in twenty-four 

 hours, so that on Feb. 15th the total bend amounted to 

 11-5 mm. Then the temperature rose but still remained 

 under 0° ; yet this rise caused a great increase in the 

 bending, as it reached the value of 9 mm. in twenty-four 

 hours (therefore 20*5 in all). Nowhere could any crack 

 or tear in the ice be seen ; the lower surface was examined 

 with particular care, and did not show the trace of a 

 crack ! 



Herr Pfaff has also succeeded in proving the expansion 

 of ice by draught. It appears therefore that near its 

 melting-point ice, like other bodies, yields to pressure and 

 to draught, and must be looked upon, particularly with 

 reference to the former, as an eminently plastic substance. 

 This behaviour of ice towards pressure at different tem- 

 peratures throws a new light upon the fact that the Telo- 

 city in the motion of glaciers increases with temperature. 

 As the glacier ice and the air over it possess a tempera- 

 ture, in the summer months at least, which lies very near 

 the freezing point, it is evident that a very small pressure 

 suffices to cause the glaciers to move. S. W. 



At present a question is being discussed by morpho- 

 logists, which seriously affects in more than one direc- 

 tion some traditional maxims of experience which were 

 apparently confirmed long ago. It treats of the way and 

 means by which cells, the foundation-stones as it were of 

 the animal organism, are formed during the first process 

 of the development of the ovum, viz., during its continu- 

 ally progressing division. The views of Remak, KoUiker, 

 and others were generally adopted and often repeated 

 until lately, namely, that the ripe and fertilised ovum, 

 when it lost its former nucleus, the "germ bubble," received 

 a new one, and that the division of this new nucleus caused 

 that of the ovum itself ; the further divisions were repre- 

 sented by the simple idea of a division of cells. Although 

 Goette already, in the year 1870 (" Centralblatt fur die 

 medicinischen Wissenschaften," No. 38), and later, 

 Biitschli (" Beitriige zur Kenntniss der freilebenden Nema- 

 toden," in " Nova acta der Leop. Carol. Deutschen Aka- 

 demie der Naturforscher," 1873), and Fol ("Die erste 

 Entwickelung des Geryonidencies ; Jenaische Zeitschrift 

 fiir Medicin und Naturwissenschaft," 1873) had opposed 

 these views on the basis of new observations, yet general 

 attention was only obtained by Auerbach in his work, 

 " Organologische Studien " (1874), as the question at stake 

 was treated in a more detailed manner. Auerbach ex- 

 amined the same animals which Biitschli had observed, 

 viz., that order of Entozoa known as Nematoidea ; he 

 found that in their fertilised ovum, after the germ bubble 

 has disappeared, two new nuclei are formed at two oppo- 

 site poles of the ovum, which then approach each other 

 towards the middle of the ovum and unite into one; this, 

 however, soon disappears again, and a less sharply de- 

 fined clear substance takes its place ; this then extends 

 longitudinally and takes a star-shaped form at each end, 

 so that the two stars are connected by a thin stem. Now 

 the division of the ovum begins to take place through the 

 middle of that stem, while in each half of the same, by 

 the confluence of little bubbles, a nucleus forms, which 

 initiates the same phenomena for the further divisions 

 as those which precede and accompany the first one. 

 The result, therefore, would be as follows : — i. In the 

 division of the ova of Nematoidta the nuclei disappear 

 before each stage of the division, and form anew after 

 each stage. 2. This formation takes place through the 

 confluence of two or more bJbble-shaped or nucleus-like 



