2^6 



Ar4 TURE 



[July 



II, 1901 



marked impression on the vividly luminous continuous back- 

 ground. Hence we conclude that the bright bands can only 

 appear with sufficient distinctness when the gyratory motion has 

 attained considerable velocity. This is exactly the sequence of 

 the phenomena observed immediately after the outburst. 



In the beginning the attracted nebular particles will impinge 

 directly on the surface of the dark body, and hence the heat de- 

 veloped will mainly serve to raise the temperature of this sur- 

 face. But after gyration has .<;et in, the direct contact between 

 the outside nebula and the body's surface is greatly lessened by 

 the interference of the vorte.x. The attracted particles will then 

 impinge upon the vortex-rings by which many of them are de- 

 flected into circular orbits and thus prevented from colliding 

 with the surface. It is therefore conceivable that the incan- 

 descence of the nucleus, after having attained a maximum very 

 soon after the collision, decreases again when the vortex motion 

 gains in power. After a time, the incandescence of the nucleus 

 will be chiefly maintained by the friction between the vortex and 

 the surface. The star's radiation must therefore ultimately attain 

 a lower limit where it becomes stationary so long as the vortex 

 motion is constant. This state appears to have been reached by 

 Nova Persei towards the middle of March. 



The variability of the star is a natural consequence of this 

 theory. We have only to .suppose that the dark body, when 

 entering the cosmical cloud, had no sensiVjle rotation of its 

 own. In this case the impacts would be more frequent, and 

 consequently the incandescence more vivid, on one part of its 

 surface than on others. Now, when the gyratory motion 

 has become considerable, the friction between vortex and body 

 must gradually impart a slow rotatory movement to the latter. 

 Thus, by rotation, the patch of greater luminosity would at 

 limes be revealed to us, while at other times it would become 

 invisible. 



In conclusion I shall mention a fact revealed by the observa- 

 tions which speaks greatly in favour of the theoretical views set 

 forth in this paper. Whenever the continuous spectrum of the 

 Nova became feeble, the green band at A = 501 was seen to gain 

 considerably in breadth and brightness. Now a reduction of the 

 intensity of the continuous background must obviously be ac- 

 companied by a decrease in the intensity of the absorption bands. 

 If the nucleus were to lose its radiating power altogether, these 

 bands would naturally become emission bands. In such a case 

 the bright bands of the spectrum would therefore appear much 

 broader and more intense. Hence any reduction in the general 

 emissive power of the nucleus must tend to increase the width 

 and brightness of the spectral lines. 



That the spectrum gradually changes from the chromospheric 

 to the nebular type is exactly what must be expected from the 

 foregoing considerations. I need scarcely say that the theory is 

 sufficiently flexible to adapt itself to any kind of hypothesis 

 which may be made with regard to the physical constitution of 

 the nebular matter. Considering the enormous forces which 

 must have been developed in the impacts, I incline to the 

 opinion that, besides a gaseous fluid, we are probably here in 

 presence of cosmical matter of a meteoritic constituency such 

 as Sir Norman Lockyer .assumes in his well-known theory. 



I am fully aware that the explanations I have been able to 

 give in this communication can only be a first approach to the 

 comprehension of a phenomenon which is necessarily one of 

 extreme complexity. Considering, however, that the theory 

 here advanced is based upon assumptions which seem to me 

 perfectly warranted and highly probable, and that the prominent 

 facts brought out by the spectroscope are satisfactorily explained 

 by it, I venture to submit it even in this preliminary state to the 

 criticism of astronomers. It is certainly the first time that 

 the ingenious theory of Dr. Siemens has been called upon to 

 explain a phenomenon in the remote recesses of the universe, 

 and I am confident there must be many admirers of this eminent 

 man of science who would wish to find his excellent theory 

 applicable to the extraordinary case of stellar evolution 

 before us, ^ 



My best thanks are due to Mr. G. Clark, of this Observatory, 

 for several suggestions which proved to be most valuable for the 

 above investigation. J. H.\lm. 



Royal Observatory, Edinburgh, June. 



1 It is worthy of remark th.Tt a terrestrial cyclone, if the velocities 

 therein exhibited were vastly greater than they actually are, and if its 

 centre were occupied by a radiating nucleus so hot as to make the gyrating 

 gases incandescent, would present to an outside observer exactly the same 

 structure in the bands of its spectrum .'■s is exhibited in the case of Nova 



■Vitality of Seeds. 



The resistance of the dormant protoplasm of seeds to low 

 temperatures has lately received much attention. C. de CandoUe, 

 Pictet, Brown and Escombe and Sir W. T. Thiselton-Dyer have 

 in succession extended our knowledge of the resistance of seeds 

 towards extremely low temperatures. The last-mentioned 

 experimenter has shown that very various seeds do not lose 

 their germinating power after being exposed to the temperature 

 of liquid hydrogen. 



The upper limit of temperature which seeds can resist does 

 not seem to have been carefully ascertained. It is probable 

 that it would vary with different seeds and for the same seed 

 when containing different percentages of water. For it is 

 known that the coagulating point of proteid depends, within 

 certain limits, on the amount of water present in it. Thus 

 Lewith (Arch, fur exp. Palhol. u. Pkarmak. 1890) showed that 

 proteid containing 25 per cent, of water coagulates at 74''-8o" 

 C, containing iS per cent, at So''-90° C, and with 6 per cent, 

 only at 145° C, It follows that if it is the coagulation by heat 

 of the proteids of the seed which prevents the embryo returning 

 from its state of suspended animation into active vitality, the 

 resistance of the seed will depend on its state of desiccation. 



With this idea I have been making a few preliminary experi- 

 ments on desiccated seeds, and I find that in every case they 

 can resist surprisingly high temperatures. At first I thought it 

 necessary to desiccate the seeds over sulphuric acid for a fort- 

 night or longer before raising their temperature considerably. 

 I now find it as effective, and more convenient, to dry the seeds 

 on an oven for a day at 65"-75" C, and then for a dav at 90° C. 

 After this they may be raised to successively higher temperatures 

 without harming them till their upper limit is passed. All the 

 seeds I have tested can resist a temperature of at least 100 C, 

 The following are the species I experimented with : — Aveiia 

 saliva, Lolium perenne, Lactitca saliva, Helianthus argo- 

 phyllus, Alimiilus moschalHS, Medicago saliva, Brassica Rapa, 

 EschschoUzia californica, Papaver somniferiim, P. muiicauU, 

 Meconopsis cambrica, Schizopetalon IValkeri. 



Of these Medicago has proved the most resistant. After an 

 exposure of one hour to 1 10° C. and then of one hour to 121° C,,- 

 10 per cent, germinated. 



■The effect of exposure to the high temperature is, however, 

 noticeable in all cases by the marked retardation of germination 

 and by the extremely slow growth afterwards. The young 

 plants, too, seem weakly, and there is a distinct loss of sensi- 

 bility to the geotropic stimulus in their radicles. Whether they 

 would ultimately become normal I cannot say, as the conditions 

 under which they were germinated were not suitable for further 

 development. 



For most of the other seeds the upper limit seems to be con- 

 siderably lower. It lies about iio"C. Perhaps, however, by 

 more careful desiccation even these less resistant ones may be 

 brought into a condition to stand exposure to higher tempera- 

 tures. The following table will convey some idea of these 

 preliminary experiments, showing the upper limit and the 

 retarding effect of exposure to high temperatures for each species. 



The Roman numerals indicate the number of days between 

 moistening and germination as indicated by the protrusion of 

 the radicle. 



NO. 1654, VOL. 64] 



From this table the increase in the time needed for germina- 

 tion is apparent. .\11 the samples of seeds were sown on moist 

 sand simultaneously, and maintained under conditions of tem- 

 perature and moisture as similar as possible. 



For the other seeds not mentioned in this table the time 

 needed for germination was not recorded, and only the maxi- 

 mum temperature resisted was observed. These maxima were 

 as follows : Schizopetalon Walkeri, 105° ; Papaver somniferttm, 

 100° ; P. nudicaide, IOO° ; Meconopsis cambrica, 100° ; Medicago 

 saliva, 121°. 



This great resistance of dried seeds to comparatively high 



