536 



NA 'JURE 



[April io, 1902 



Formula for the Perimeter of an Ellipse. 

 WiLi, one of your mathematical readers kindly state whether 

 the following empirical formula gives a nearer approximation to 

 the perimeter of an ellipse than that usually given in pocl;et- 

 Ix)oks of formula; ? 



-v and y stand for axes. 



r loc 2 log 3 ~\ loc Tf - 'og 2 



I ,.log IT - log .1 ^ j,log IT - log 2 I loi; :• 



Perimeter = -n - — r 



where light is evolved except through the medium of 

 heat, yet in nature, by a simple cell, light is produced 

 which is apparently unaccompanied by any invisible 

 radiations whatever. 



These organisms are sometimes referred to as "phos-' 

 phorescent," but the term is hardly a suitable one, as the 

 phenomenon is likely to be regarded as analogous to the 

 emission of light by inert chemicals and minerals, or to 

 the continued glow of vacuum tubes after an electrical 



Molesworth's Ijoak gives the followint; : — 

 T = semi-major axis ; C — semi-minor axis. 



Perimeter := Air[N/2(T- + C^) -f T -)- C] + 0'207S(T - C). 



State School, Beaudesert, H. Tomkys. 



Nr. Brisbane, Queensland, Australia, February 26. 



Sounds Associated with Low Temperatures. 



There is one place where the sounds mentioned by Mr. 

 Cave (p. 512) can be (or used to be) heard to perfection. This 

 is at the lower end of Beaumont Street, Oxford, where the road 

 widens out in approaching Worcester College. The pavement 

 and the fence adjoining it take a crescent form, and while walk- 

 ing on the former quite a loud metallic musical note may 

 always be heard. The fence consists, or consisted, of boards, 

 in front of which are iron palings, the uprights of which had 

 a square section. Sl'ENCiiK Pickerinc. 



Woolacombe. 



Sun Pillars. 



This evening a sun-pillar was again visible at Swindon, not 

 so brilliant or long-lived as that which recently attracted such 

 widespread attention, but nevertheless quite definite. I first 

 observed it about 6.15 p.m., when the sun was a few degrees 

 above the horizon. It was of a clear yellow colour, and 

 extended from the dull-red sun vertically upwards. The sun 

 set behind a bank of murky haze, and shortly after — about 6.45 — 

 the pillar had faded from view. H. B. Knowles. 



Swindon, .\pril 7. 



L UMINO US BA CTERIA 

 T UMINOUS bacteria constitute a group of organisms 

 -•— ' which under certain conditions have the power of 

 emitting light. They occur principally, if not entirely, in 

 sea-water. It is, however, doubtful whether they give 

 rise to any general luminosity of the sea, such as is 

 caused by noctiluca and other relatively high forms of 

 marine life, although it is possible that in the tropics, 

 where the amount of non-living nutriti\e material is 

 present in sufficient quantities, that bacteria do occasion- 

 ally cause a general luminosity; but the opportunities of 

 verifying this are rare. One organism in particular, the 

 Pholobactcriuiii IndicuDi, from its forming a surface 

 pellicle in artificial fluid cultures, which is very luminous, 

 may at times cause luminosity of sea-water at the surface. 

 It is remarkable th.it an unicellular organism such as a 

 bacterium should have the power of emitting light. 

 There is no evidence of any special structure in the cell 

 itself, and in the present state of our knowledge it is 

 difficult to regard it as other than a result of functional 

 activity, exactly as heat is evolved by other forms of 

 life, as an accompaniment of the metabolism of the cell. 

 What is, however, the exact difference between the evolu- 

 tion of heat by some organisms and that of lij^ht loy others 

 it is at present impossible to say. Oxygen is absorbed in 

 both instances and carbon dioxide evolved, but there is 

 evidently some other factor of which at present we know 

 nothing. The fact that light and heat are manifestations 

 of the same form of energy may apparently simplify the 

 rnatter ; but further consideration shows that there is a 

 different problein to be solved in each. 



We are not acquainted with any artificial method of 

 light production, in which chemical action takes place, 

 NO. 1693, VOL. 65] 



current of high potential has been passed through them. 

 In all marine light-producing animals, the light is not 

 emitted continuously, but is given out at intervals in 

 response to some stimulus or irritation. It is possible 

 that bacteria act in the same way, but it is difficult to 

 determine this point, as the individual organism is not 

 sufficiently luminous to enable the observer to study it 

 under the microscope by its own light. In fluid cultures 

 they apparently respond to any agitation or excitation so 



-CultuicsoldilTerent: 



long as the supply of oxygen is maintained, but they 

 can be kept in a luminous condition on fluid media if 

 oxygen is continuously supplied in other ways, although 

 they may remain at rest. 'Phis can be done, for instance, 

 by allowing the wool plug, used to close the orifice of 

 the glass vessel containing a fluid culture, to become 

 saturated with the culture, when the plug will continue to 

 glow for days, altliough llie culture in the vessel may 

 only become luminous when agitated. This points to 



