NATURE 



[August io, ign 



genous to the district. When detected, such supposed 

 grass-blades are the yellow head-stripes of the snipe. If 

 surprised on a patch of green turf or other inharmonious 

 background, the bird will sometimes run and squat on the 

 mud near a patch of herbage close at hand. 



It is announced in the July number of British Birds, by 

 Mr. A. H. Meiklcjohn, that a breeding colony of fulmar 

 petrels has established itself in Berriedale Head, Caithness, 

 the only other nesting haunt on the mainland being Cape 

 Wrath, Sutherland, which was first discovered to be the 

 resort of these birds in iqoi. The most southerly breeding- 

 place in the British Isles is Barra. 



Certain erratic lights observed at night on the hillsides at 

 Villierstown ferry, Cappoquin, Ireland, during last winter, 

 by Miss M. E. Dobbs and the local ferrvman are tentatively 

 attributed by the former, in an article published in The 

 Irish Naturalist for July, to luminous owls, this opinion 

 being based on the assertion of the aforesaid ferryman that 

 the lights are due to birds. In a supplementary article 

 published in the same issue, Mr. C. B. Moffat, after 

 quoting additional testimony io the belief that birds rre 

 their source, suggests that these strange luminous emana- 

 tions may be a form of ignis fatuus. It is true that the 

 latter i« generally a more flickering type of light, but one 

 resembling Miss Dobbs's description is reported from the 

 Donnhate estuary, unless, indeed, the natives mistake a 

 bird for a phantom. But Mr. Moffat goes even further 

 than this, and suggests that the whole story of luminous 

 owls, which, it will be remembered, was first reported bv 

 Sir Digby Pigott in a letter to The Times for December, 

 IQ07, may possibly turn out to be a myth. He notes, 

 however, that an apparently similar luminosity has been 

 attributed to bitterns and certain herons, especially an 

 American species, but states that even this testimonv is not 

 definitely accepted by naturalists. 



Among the contents of the July number of the Journal 

 of the South African Ornithologists' Union is an article by 

 Mr. C. F. M. Swynnerton on nests and eggs from Mount 

 Chirinda, southern Rhodesia. 



IONISATION AND CHARGED SMOKE 

 PARTICLES. 

 TN the Sitzungsberichte der k. Akad. der Wissenschaften 

 of Vienna, vol. 120, part i., Drs. V. F. Hess and G. v. 

 Sensel discuss the results of a series of experiments on the 

 ionisation of the atmosphere made by them during August 

 and September, 1909, on an island separating the two 

 branches of the Danube near Vienna. The observations 

 were made from 9 a.m. to 9 p.m., and the curves for the 

 diurnal variation show marked minima about 5 p.m., both 

 for the positive and for the negative ions. The main 

 object of the authors was to investigate the connection 

 between the ionisation and the meteorological elements, 

 but the period of observation was too short for the conclu- 

 sions to be regarded as final. The principal results are 

 briefly as follows. For low atmospheric pressure the excess 

 of positive ionisation has double its value at ordinary or 

 high pressures, and a similar difference exists between the 

 values for falling and for rising barometer ; the total 

 number of ions, and the number of negative ions, decreases 

 as the temperature increases — a result exactly opposite to 

 that found by Simpson and Gockel : the number of ions 

 is greater for clear than for cloudy sky, especially if the 

 cloud is nimbus : the number of ions" is less when the 

 wind comes from the direction of the city ; and it is in- 

 dependent of the relativi humidity, a result also different 

 from those of Simpson and Gockel. who found that the 

 ionisation decreased as the humidity increased. The recent 

 establishment of systematic observations of the ionisation 

 at some of the principal observatories ought to permit of a 

 fuller discussion of the questions treated in this paper, 

 which will prove valuable in indicating the observations 

 which are specially desirable. 



The same number contains a discussion by Dr. K. 

 Przibram of experiments on the charge carried by smoke 

 particles, in the light of Cunningham's correction to Stokes' 

 formula for the connection between the limiting velocity 

 and the radius of the particle. Careful series of experi- 

 ments on smoke of different substances indicated a definite 

 tendency for the charge to depend on the radius of the 



NO. 2l8o, VOL. 87] 



particle, and led the author to conclude that the particles 

 could carry charges less than the adopted value for the 

 charge on the negative ion, or that certain factors entered 

 into the motion of charged particles through a gas which 

 had not yet been allowed for. In a note added after the 

 paper had been printed, the author states that owing to a 

 criticism by Regener, he repeated some of the experiments 

 with the plates of his condenser closer together, when he 

 found much less dispersion in the values for the charge. 

 Consequently, the conclusions founded on the earlier experi- 

 ments may be subject to modification. 



HIGH-PRESSURE WATER-POWER WORKS.' 

 'THE utilisation of high-pressure water-powers represents 

 the latter portion of the wonderful and rapid develop- 

 ment which has occurred in hydraulic works during the 

 last twenty years. Such powers are necessarily situated in 

 mountainous districts, and may be at some considerable 

 distance from thickly populated centres where a demand 

 for power exists. Comparatively low falls were more in 

 use until the question of long-distance high-tension elec- 

 trical transmission could be looked upon as a sound 

 technical and commercial proposition, and this has only 

 been satisfactorily solved within the last few years. 



Hydro-electric stations do not lend themselves very 

 readily to hard-and-fast rules. It by no means follows 

 that what has shown itself to be satisfactory in one case 

 will be equally satisfactory in another. Engineers of every 

 branch are represented in work of this kind, besides 

 surveyors, architects, miners, railroad men, and in some 

 cases geologists and also meteorologists have to be 

 consulted. High-pressure plants usually work out con- 

 siderably cheaper than low-pressure plants for the same 

 power, but a long transmission line may so increase the 

 capital outlay on the former that a low-pressure station 

 near the consumer is preferable. A very great advantage 

 possessed by high-pressure plants over other types is the 

 readiness with which the irregular flow of rivers may be 

 regulated to supply a constant-power demand by means of 

 storage reservoirs and weirs. The whole rainfall of a 

 district may thus be utilised. Storage, how-ever, increases 

 the cost of a station very considerably. The greater the 

 head of water, the more rational will a storage reservoir 

 be, since the same quantity of accumulated water will 

 represent a proportionately larger store of energy. 



Too little attention is usually devoted to the pipe-lines 

 and conduits carrying the water from the lake or river to 

 the turbines. Not a few engineers consider that the pipe- 

 line is a secondary part of a hydraulic power-plant. Pipe- 

 lines are often built by engineers who are experts in the 

 choice of material and in the manufacture of a pipe, but 

 who do not understand the essentially important functions 

 which a complete pipe-line, and especially a high-pressure 

 pipe-line, has to fulfil. The general arrangement, the 

 relative dimensions of different parts of the pipe-line, the 

 methods of anchoring and placing of fixed points, are all 

 such important factors that they can only be prop'iU 

 determined by the turbine builder. 



The Necaxa power-station of the Mexican Light and 

 Power Co. is supplied with water under a head of ni2 

 feet from a reservoir having a capacity of 1500 million 

 cubic feet. The first part of the scheme, commenced in 

 1903, consisted of the construction of a large earth dam 

 above the falls of the Necaxa River to form the storage 

 reservoir which supplied the power-station with water for 

 about 50,000 horse-power. The dam has a maximum 

 height of 197 feet, length 1270 feet, and greatest breadth 

 at the base 051 feet. An earth dam was selected as the 

 type most suitable for a country periodically liable to 

 earthquakes. Two feeder pipes 6 feet in diameter start 

 from the intake tower in the lake and pass through a 

 tunnel which emerges below the dam wall. These pines 

 are made of riveted plate, and pass to a receiver pine 

 which is under a pressure head of 177S feet. Six high- 

 pressure pipes descend from the receiver to the power- 

 house. Sluice valves are provided at the receiver to 

 control each pipe, and air pipes are laid from behind the 

 valves on each high-pressure pipe up the hill to a height 



1 Abstract of a paper rernl :u the summer meeting at Zurich of the Insti- 

 M Mr. I.. Zodel, of Zurich. 



