96 



NATURE 



[November 17, 19 10 



reiyjonsible for the trouble. When the focus is at a white- 

 dot image the white lines must be counted, and vice versd, 

 when the focus gives a black-dot image. — E. M. Nelson : 

 The resolution of new detail in a Coscinodiscus astcrom- 

 phalus. This paper has refeience to the resolution of 

 further detail obtained by a new one-eighth objective by 

 Zeiss, described in a previous communication. The new 

 detail discovered is a fine sieve covering the so-called eye- 

 spot in C. asteromphalus. As the size of the eye-spot is 

 only I '14,000th of an inch, it may be left to the imagina- 

 tion to estimate the size of the minute perforations form- 

 ing the sieve. 



Physical Society, October 28.— Prof. H. L. Callendar, 

 F.R.S., president, in the chair. — Prof. Ernest Wilson and 

 \\". H. Wilson : A new method for producing high tension 

 discharges. According to this method energy is taken from 

 an alternating or continuous current source and stored in 

 a magnetic field by an inductance ; it is then permitted to 

 surge into a condenser which forms with the inductance a 

 lo'cv frequency- oscillating circuit. When the energy is 

 stored in the condenser the latter is mechanically bridged 

 across the primary winding of a spark-coil, with which it 

 forms a high frequency oscillatory circuit. The energy 

 is then transmitted by the secondary winding of the spark- 

 coil to the work circuit in the well-known manner. Briefly 

 the following are some of the advantages gained : — (i) For 

 X-ray work the inverse electromotive force at " make " is 

 eliminated, thereby leading to increased life of the tube and 

 to a more sharply defined radiograph. (2) Only a small 

 magnetising current is required as the inductance has a 

 nearly closed magnetic circuit. This gives rise to a very 

 small C'R loss and consequently higher efficiency. (3) On 

 account of the long periodic time of the system between 

 the periods of "break" and "short-circuit," the voltage 

 across the contact of the interrupter at " break " does not 

 rise to a high value, or rises so slowly that the contacts 

 are well separated before it is developed. Hence immunity 

 from sparking. (4) The method lends itself to few second- 

 ary turns and this keeps down the time constant. It also 

 makes the coil lighter, cheaper, and more compact. 

 (5) The method lends itself to low secondary resistance — a 

 point of great importance in connection with radio-tele- 

 graphy. (6) The iron of the spark-coil can be kept small 

 in amount, and special attention can be paid to its lamina- 

 tion and insulation, as it may have to be operated at 

 frequencies of three or four thousand per second. (7) The 

 elimination of sparking increases efficiency, and on board 

 ship where coal gas is not conveniently obtainable this is 

 an advantage. (8) The apparatus can be worked from 

 direct-current or alternating-current systems at usual 

 voltages, or from a portable battery of a few storage-cells. 

 (9) The oscillatory current at " break " does not pass 

 through the battery, and hence does not assist in its dis- 

 charge. (10) The iron in the magnetic circuit of the 

 external inductance has only to operate at low frequency, 

 and hence it has not to be finely laminated. (11) When 

 used on alternating-current systems, rectification, if 

 desired, is easily effected by employing two short-circuiting 

 brushes, one for each half-period, and allowing the second 

 brush to short-circuit at the moment when the condenser 

 is fully charged after allowing a second complete surge 

 of the energy between the condenser and the inductance 

 of the spark-coil. (12) The apparatus is light, efficient, 

 and cheap, and is suitable for radio-telegraphy. X-ray, 

 medical, and other work in which high-tension electricity 

 is f-mploved. — F. Rogers : The behaviour of steel under 

 combined static stress and shock. Attention is directed to 

 the importance of the time rate of increase of stress, 

 ds/dt, in the behaviour of materials under stress. The 

 . exact determination of this rate must usually present much 

 difficulty, but the indirect experimental method adopted 

 consisted in submitting specimens of steel to shock whilst 

 under static loading. The conclusion that steel is sub- 

 stantially less resistant to shock whilst it is under static 

 stress appears to be definitely established. In some cases 

 the effect of a large static stress was to diminish the 

 resistance to shock by as much as 30 per cent. The 

 correction for the work done upon the sample in applying 

 the static load is relatively small. Thus the energy 

 absorbed in breaking a sample of steel is greater when 

 entirely applied as shock than when applied partly as 



NO. 2142, VOL. 85] 



shock and partly statically. This difference is considered 

 to be due chiefly to the difference in the rate of increase 

 of stress at the higher stresses in the two cases. The 

 actual values of the highest stresses are not necessarily 

 identical, but probably the higher the rate of increase of 

 stress the higher is the greatest stress reached before 

 rupture occurs, whilst, simultaneously, deformation is 

 diminished, and the intimate nature of the breakdown 

 suffers a corresponding variation. At the higher static 

 loads employed some portions of the test-pieces were 

 stressed beyond their elastic limits, and this may also help 

 to account for a part of the diminution in resistance to 

 shock. 



Linnean Society, November 3.— Dr. D. H. Scott, F.R.S., 

 president, in the chair. — Prof. W. A. Herdman : A com- 

 parison of the summer plankton on the west coast of 

 Scotland with that in the Irish Sea. This paper is the 

 result of a series of vertical plankton hauls taken with 

 the " Nansen " closing tow-net (made of No. 20 silk) from 

 the S.Y. Ladybird in July of the last four years, from 

 various deep hauls (eighteen of them being from more 

 than 100 fathoms) at various localities off the west coast 

 of Scotland. A comparison of the collection shows 

 (i) that there is a constancy year after year in the nature 

 of the plankton at certain localities ; and (2) that some of 

 the localities, not very far apart, differ considerably from 

 one another in the nature of their plankton at the same 

 time of year (July). Some of these deep hauls consist 

 markedly of zoo-plankton and others of phyto-plankton, 

 and the latter show a close resemblance to the phyto- 

 plankton hauls typical of the vernal maximum of diatoms 

 in the Irisli Sea. The complete disappearance of the 

 phyto-plankton, which is such a marked feature in the 

 summer (July and August) gatherings from the Irish Sea, 

 does not seem to take place in some localities off the west 

 coast of Scotland, and these phyto-plankton hauls are 

 obtained, not in the deep fiord-like lochs, but in the open 

 sea, e.g. off Ardnamurchan and off the islands of Rum 

 and Canna in the Sea of the Hebrides. — J. C. F. Fryer : 

 The structure and formation of Aldabra and neighbouring 

 islands, with notes on their flora and fauna. Aldabra, 

 situate 250 miles north-west of Cape Amber, is a large 

 atoll with an almost complete land-rim, a large shallow 

 lagoon, and a narrow fringing reef. The land-rim is 

 composed of coral-limestone, which gives definite evidence 

 that Aldabra was formed by elevation and once stood at 

 more than 40 feet above sea-level, though rain-water 

 denudation has reduced this to its present level of 15 feet. 

 A deposit of guano, by combination with the limestone, 

 has produced phosphatic rocks, interesting in that they 

 prove that the lagoon was once non-existant, and has 

 since been formed by erosion and denudation. The atoll 

 is still being washed away, but the loss is in part com- 

 pensated b}' the piling up of sand by wind and wave. The 

 fauna and flora, though peculiar, have been largely derived 

 from Madagascar, the flora being interesting in showing 

 four distinct types of jungle. Assumption, Cosmoledo, 

 Astove, are also islands and atolls of elevated coral-rock, 

 and form an interesting series showing the loss of rock- 

 land by erosion and its replacement by sand and clays. 

 Giant land-tortoises still exist on Aldabra, and fossil re- 

 mains were found on the three other islands visited ; in 

 this connection it is noteworthy that none of these islands 

 has ever been connected with continental land. — H. B. 

 Bigrelow : The Siphonophora of the Research Biscayan 

 plankton. The memoir forms the thirteenth report on 

 Biscayan plankton collected on board H.M.S. Research 

 in 1900. The collection consisted exclusively of Calyco- 

 phoridfe, with the exception of a single fragment from 

 another group. In his report of the Siphonophora of the 

 National, Prof. Chun noted a similar absence of Physo- 

 phoridaj during the North Atlantic summer, and suggested 

 that these latter forms must be at considerable depths at 

 that season, yet the numerous hauls of the Research with 

 closing nets down to really great depths failed altogether 

 to find them. On the other hand, it is only during 

 summer that these Physophoridae are found on the eastern 

 coasts of North America, at a time when the cold current 

 alongshore- is at its warmest : and further, they were not 

 uncommon in July and August during cruises of the 

 Research in the Fseroe Channel, in the cooler water of 



