August 19, 1880] 



NATURE 



Z77 



of Irkajpij. Hence it follows that the algal flora differs in its 

 composition in a noteworthy degree in the eastern and western 

 portions of the Siberian Polar Sea. 



It has been stated that an abundance of large-sized luxuriant 

 plants is a characteristic of the Arctic algae. In this respect 

 the vegetation of the Siberian Sea is considerably behind that in 

 other parts of the North Polar Sea. The largest alga seen by 

 Dr. Kjellman was a Laminaria Agardhii, whose length was 210 

 and greatest breadth 37 centimetres. Among the many speci- 

 mens of L. cunei/oHa examined there was none more than half 

 so large as this. L. soli.hingula is about as large as middle- 

 sized specimens of this plant from the coasts of Spitzbergen and 

 Novaya Zemlya, about 90 centimetres long and 15 to 20 broad. 

 The two species of Alaria, when they are largest, are about a 

 metre in length. Other alga: almost without exception are 

 stunted in comparison with plants of the same species from other 

 portions of the North Polar Sea. 



The collections of algae made by Dr. Kjellman, according to 

 the examination to which it has been possible to subject them, 

 consist only of thirty-five species, of which there belong to tlie 



Floride-Te ... 12 



Fucoidece 16 



Chlorophyliophycese 6 



Phycochromophyceae I 



These are not more tb.an half as many as are known from the 

 Murman and Spitzbergen Seas. With the exception of two, or 

 possibly three, species, all also occur in other parts of the North 

 Polar Sea. 



The western part of the Siberian Polar Sea, at least to Cape 

 Chelyuskin, must douhtless be considered to belong to the terri- 

 tory of the Spitzbergen marine flora, though poorer in indi- 

 viduals and species and more stunted than it. The algae in 

 the eastern part of the same sea also in a considerable degree 

 correspond with those on the coasts of Spitzbergen and Novaya 

 Zemlya, but in the composition of its Laminaria vegetation it has 

 a trait foreign to the latter, and indicating a connection with the 

 algze in the north part of the Pacific. 



ON THE COMPRESSIBILITY OF GLASS ^ 



'T'HE following experiments were undertaken with a view to 

 ■^ determine by actual observation the effect produced on solids 

 by hydraulic pressure. The instrument was constructed accord- 

 ing to my directions by Mr. Milne, of Milton House, about two 

 years ago, but it is only now that I have been able to devote 

 myself to its application to the purposes for which it w'as de- 

 signed. It consists of a hydraulic pump, which communicates 

 with a steel receiver capable of holding instruments of consider- 

 able size, and also with a second receiver of peculiar form. This 

 receiver consists essentially of a steel tube terminated at each 

 end by thick glass tubes fitted tightly. It is tapped at the 

 centre with two hole?, the one to establish connection with the 

 pump, and the other to admit a pressure-gauge or manometer. 

 The steel tube may be of any length, being limited only by the 

 extent of laboratory accommodation at disposal. The tube 

 which I am using at present has a length of a little over si.x feet, 

 and an interna! diameter of about three-tenths of an inch. The 

 solid to be experimented on must be in the form of rod or wire, 

 and must, at the ends at least, be sufficiently small to be able to 

 enter the terminal glas^ tubes, which have a bore of o'oS inch, 

 and an external diameter of o'42 inch. The length of the solid 

 is such that when it rests in the steel tube its ends are visible in 

 the glass tenriinations. 



When the joints have all been made tight the experiment is 

 conducted as follows : — 



!; A microscope with micrometer eyepiece is brought to bear on 

 each end of the rod or wire. These microscopes stand on sub- 

 stantial platforms altogether independent of the hydraulic appa- 

 ratus. The pressure is now raised to the desired height, as 

 indicated by the manometer, and the ends of the rod are observed 

 and their position with reference to the micrometer noted. The 

 pressure is then carefully relieved and a displacement of both 

 ends is seen to take place, and its amplitude noted. The sum of 

 the displacements of the ends, regard being had to their signs, 

 gives the absolute expau.ion in the direction of its length, of the 

 glass rod, when the pressure at its surface is reduced by the 

 observed amount, and consequently also by the compression 

 when the process is reversed. As in the case of non-crystalline 

 Ixidies, like glass, there is no reason why a given pressure should 



^ S.:bstance of a paper read before the Royal Society of Ed-nburgh. 

 June 21, by J. Y. Buchanan. 



produce a greater effect in one direction more than in another, 

 we may, without sensible error, put the cubical compression at 

 three times the linear contraction for the same pressure. 



As yet I have only experimented on glass, and only on one 

 sort, namely, that made by Messrs. Ford and Co. of Edinburgh. 

 It contains lead, and is very suitable for glass-blowing pm-poses. 

 I have not yet analysed it. I have observed its compressibility 

 up to a pressure of 240 atmospheres, and before proceeding to 

 higher pressures I intend to determine the compressibilities of 

 other solids, especially metals at pressures up to 240 atmo- 

 spheres. The reason for taking this course is that having got 

 two glass tubes to stand this pressure I am anxious to utilise 

 them as far as possible before risking them at higher pressures. 



The pressure in these experiments was measured by a mano- 

 meter, which consists simply of a mercurial thermometer with a 

 stout bulb, which is immersed in the water under pressure, whilst 

 its .stem projects outside. 



The values of the readings of this instrument were determined 

 by comparing it with a piezometer containing distilled water. 

 This piezometer had been compared with others which had been 

 subjected to the pressure of very considerable and measured 

 columns of water on the sounding-line. 



The mean apparent compressibility of water in glass was thus 

 found' to be o'0O0O4868, or, multiplying by 1,000, to reduce the 

 number of figures o'04S6S per atmosphere at temperatures from 

 1° to 4° C. 



The manometer (No. 2) was compared with this piezometer. 

 The temperature of the manometer was I2''"S C, while the 

 piezometer was enveloped in ice in the receiver. The ice was 

 thus melting under the same pressure as the instrument was 

 undergoing, consequently the piezometer was not exposed really 

 to precisely the same temperature at each succeeding experiment. 



For our present purpose the effect of the possible variation in 

 volume due to this thermic cause is negligable, and we assume 

 that the indications of our piezometer are comparable with those 

 obtained in deep ocean waters. In a future communication I 

 hope to return to this point. 



In Table I. we have in the first column the number of obser- 

 vations meaned for each pressure from which the average values 

 of the manometer-reading under A, and of the piezometer- 

 indication under H are computed. 



Manometer No. 2, when treated simply as a thermometer, 

 showed at atmospheric pressure a rise of one division for a rise 

 of o'233° C. in temperature. Piezometer K, No. 4, was filled 

 with distilled water, and contained 774 cubic centimetres at 0° 

 and atmospheric pressure. It is made of Ford's glass, though 

 not drawn at the same date as the experimental rod. 

 Table I. — Comparison of Manometer No. 2 at I2'5° C. with 

 Piezometer K, No. 4, in ice melting under pressure 



Dividing the mean apparent contraction of the water in the piezo- 

 meter by the apparent compressibility of water in glass (0-04S6S), 

 we have for the pressure corresponding toariseof 43-61 divisions 

 on manometer No. 2 at 12-5° C. 



P = _i? — = -^?4 = 136-6 atmospheres. 



0-04868 0-04868 ^ 



< Proc, Royal Society of London, 1876. p. 162. 



