37? 



NATURE 



[September 14, ign 



We should prefer to place the models illustrating the 

 crystal-systems on a lower shelf, rather than to tilt some 

 of them in order to show their lateral axes. The features 

 of the optical indicatrix are well illustrated by hoops and 

 wires. The explanations of the models serve as an intro- 

 duction to the examination of mineral-slices with the 

 polarising microscope ; but we may prefer the generalised 

 diagrams of Groth to those here given for a special case. 

 There seems an arrow-head too many in one of the figures ; 

 and we doubt if Mr. Lowe's model has, as he states, the 

 short diagonal of the analysing nicol " inclined towards 

 the observer at an angle of 45 with the horizontal plane." 



For several years past the Aire and Calder Navigation 

 Company has been improving the navigation along the 

 system of canals between Goole and Leeds by deepening 

 and widening the water-way ; and in consequence the 

 traffic has been very largely increased, rendering Leeds 

 an inland port on a small scale. Recently a steamer 

 So feet long reached Leeds from the docks at Hull in 

 nineteen hours. 



An automatic stabilisator, recently invented by M. 

 Doutre, has been used with partial success on a Farman 

 biplane in France, where it has aroused considerable 

 interest. It is designed solely for preserving fore-and-aft 

 equilibrium, and one of its most interesting results is to 

 give the machine to which it is fitted its best angle of 

 glide independently of the pilot's control. The apparatus 

 consists of two parts, an anemometer and what is termed 

 an " accelerometer. " The former is a plate placed 

 normally to the air-flow, and backed by two springs of 

 such a strength that the pressure on the plate, when the 

 machine attains its mean speed, entirely compresses them. 

 The forward motion of the plate resulting from any 

 diminution of the wind-pressure depresses the elevator 

 through the agency of a piston operating by compressed 

 air. The " accelerometer " consists of two movable and 

 relatively heavy cylinder-heads, each sliding on a rod 

 placed end on to the flight-path, which move under inertia 

 whenever the speed of the machine diminishes or increases, 

 and operate the elevator in a similar way to the anemo- 

 meter. These cylinder-heads are held at each end by 

 springs, which return them to their initial position when 

 the aeroplane progresses at a uniform speed, and also 

 check their movement when the machine pitches without 

 speed variation. Both the accelerometer and the anemo- 

 meter have been combined in one instrument by the 

 inventor, and experiments in calm weather proved that the 

 machine could safely fly for several seconds uncontrolled. 



An interesting article on engineering problems in 

 Nicaragua, by Mr. T. Lane Carter, appears in The 

 Engineering Magazine for August. As few countries have 

 such a rainfall as one finds in Nicaragua, irrigation is not 

 one of these problems. At Greytown, at the mouth of the 

 San Juan River, the rainfall is about 300 inches per 

 annum ; in the mountains, where the gold mines are 

 situated, the rainfall varies from 100 to 125 inches per 

 Milium. With rainfall and soil such as they have in 

 Central 'America, it is not surprising that the vegetable 

 growth is rapid. Two and a half crops of corn can be 

 raised per year. Sugar-cane will produce there for seven 

 or eight years, and does not need an annual planting, as 

 in Louisiana. But the agricultural engineer will find a 

 great deal to occupy his attention in Nicaragua. In the 

 eastern part of the country agriculture is in as backward 

 a condition as in the days of Columbus. Take, for 

 instance, the usual method there of planting corn. A patch 

 is selected in the forest, and the trees and hushes Felled. 

 NO. 2185, VOL. 87] 



No attempt is made to clear away the rubbish. A man 

 goes round with a sharp, pointed stick, pokes holes in the 

 ground wherever he can find a place amongst the debris, 

 drops in a few seeds, and leaves the crop to nature's care. 

 There is no hoeing or cultivating done. The corn must 

 fight out its battle unaided by man. Strange to say, the 

 crop is gathered in about eight weeks. 



A leading article in Engineering for September 1 deals 

 with the recent investigation on the stress distribution in 

 a plate pierced with a hole and subjected to pull, which 

 has been ably carried out by Dr. K. Suyehiro, of the 

 Department of Naval Architecture, Tokio University. 

 Strictly speaking, the solution appertains only to the ideal 

 case of a plate pierced at the centre and extending to 

 nfinity in all directions ; this is assumed to be subjected, 

 n one direction only, to tension, the distribution of which 

 s uniform at an infinite distance from the origin. Dr. 

 Suyehiro then works out what the distribution of stress 

 is in the immediate neighbourhood of the hole, and finds 

 that the maximum value of the stress is no fewer than 

 three times that of the average value. If there were any 

 real analogy between stream-lines and stress-lines, the 

 maximum stress, he points out, would be double the mean. 

 Dr. Suyehiro also shows that local concentrations of stress 

 have practically vanished at points distant from the centre 

 of the hole by 15 radii ; hence his result is applicable to 

 quite narrow plates. He has also compared the results of 

 his calculations with direct experiments on a strip of india- 

 rubber, and finds remarkably close agreement. In view of 

 the importance of the fact that a ship's deck is under push 

 and pull alternately, a useful investigation might be made 

 on the elastic breakdown and final rupture of a wide bar 

 pierced with a hole and subjected to alternating stresses of 

 push and pull. The original paper is reprinted in full in 

 the issue of Engineering already quoted. 



OUR ASTRONOMICAL COLUMN. 



Kiess's Comet, 1911b. — No. 4522 of the . Astronomische 

 Nachrichten contains a new set of elements calculated by 

 Dr. H. Kobold for comet 191 16, also a number of observa- 

 tions of the comet. The observations, made about the 

 middle of August, are somewhat uncertain, owing to the 

 difficulty of the object, and Senor Marisonza reports from 

 Rio de Janeiro that during August 18-20 the brightness 

 had rapidly decreased ; he states that it could not be 

 observed there after August 24. The ephemeris computed 

 by Herr A. Kobold shows that the present magnitude 

 should be about 8-6, and the position for September 14 is 

 i8h. 15.3m., —45° 24-1'; the comet is now nearly stationary 

 in Corolla, immediately north of a Telescopium. 



Meridian Circle Observations. — From the Harvard 

 College Observatory we have received vols. lxv. and lxvi. 

 of the Annals, embodying the journal of the zones observed 

 with the 8-inch meridian circle during the years 1888-90 

 and 1890-8 respectively. The observations were made and 

 the volumes prepared by Prof. Searle in the preparation 

 of a catalogue which is to appear in vol. Ixvii. of the 

 Annals; a previous publication, vol. lx.il . , part i., dealt 

 with the fundamental stars employed in the same zone, 

 viz. — 9 50' to — 14 10'. 



Brooks's Comet, 1911c. — The brightness of Brooks's 

 comet, iquc, continues to increase, and during the fine 

 nights recently experienced at Portsmouth many British 

 Association visitors who are not astronomers found no 

 difficulty in distinguishing the comet from the surrounding 

 stars merely by naked-eye observations. According to the 

 supplement to No. 4522 of the Astronomische Nachrichten, 

 Dr. Schiller reports that on August 29 the comet was about 

 half a magnitude fainter than the Andromeda nebula. Its 

 nucleus, formerly sharply stellar, had become diffuse, and 

 in a bright red field was well seen. Dr. Ebell found that 

 on August 26 the brightness of the comet was comparable 



