62 



NA TURE 



[Afay 19, 1887 



of hull, from the flatness of bottom and fullness of ends ; 

 (2) weakness of action of rudder, from its position in the 

 dead-water ; (3) an active turning force, consisting in a 

 one-sided pressure on the stern arising out of a one- 

 sided system of flow in the water closing in behind 

 the full run. It was principally to the last-mentioned 

 cause that Mr. Froude, when called upon to investigate 

 the case of the Ajar, was inclined to attribute the 

 behaviour of the ship, such a phenomenon having been 

 some years since incidentally observed in the course of 

 experiments made in the experiment tank at Torquay on 

 the resistance of a model having a full run. In this case 

 a lateral force was found to be developed upon the stern of 

 the model, accompanied by a trailing away of the wake to 

 one side, and a transverse flow of the water across behind 

 the stern, in the opposite direction to that in which the 

 lateral force was developed. This one-sidedness of flow, 

 and consequent force (like the helm tendency of the AJax), 

 was sometimes in one direction, and sometimes in the 

 other, and occasionally reversed its direction during any 

 experiment ; but was generally more or less persistent in 

 direction when initiated, although the direction in which 

 it was initiated was apparently a matter of accident. It 

 was Mr. Froude's belief, founded on these and many 

 other experiments of various kinds, that this species of, 

 so to speak, spasmodic one-sidedness of flow, and con- 

 sequent one-sided force, attends the motion of all, 

 even perfectly symmetrical, bodies through water, when- 

 ever their leaving lines are blunt enough to cause a large 

 eddy behind them. 



By way of a method of experiment suitable to test the 

 efiect of remedies designed to mitigate or remove either 

 of the three presumable causes of the behaviour of the 

 ship, which have been enumerated above, Mr. Froude 

 towed a model of the Ajax in the experiment tank at 

 Torquay, the model being attached to the towing carriage 

 in such a way that, while the model was free to sheer out 

 of the straight course, any such attempted sheering 

 motion actuated a working rudder fitted to the model, in 

 the proper direction for frustrating the attempt. By this 

 contrivance the model was made to steer quite straight, 

 and the criterion of the badness of the steering qualities 

 of the model in the several conditions of trial subjected 

 to experiment, was the amount and the degree of un- 

 steadiness of the helm angle administered, this'helm angle 

 being continuously recorded throughout each experiment 

 by an automatic apparatus. Thus tested, the model was 

 found to exhibit conspicuously what has been referred to 

 as the predominant characteristic of the behaviour of the 

 ship, viz. the large helm angle, sometimes persistently 

 on one side, sometimes on the other, and occasionally 

 changing from one side to the other. 



The principal remedies tentatively applied to the model 

 y\ath a view to identifying the main source of the evil, and 

 indicating the direction in which improvement was to be 

 sought, were these : (i) a deep keel, to supply "the directive 

 character " m which the hull itself was presumably lacking ; 

 (2) placing the rudder altogether below the keel, so as to 

 be quite clear of the dead-water ; (3) an extensive dead- 

 wood (or fixed rudder) behind the stern-post, (the working 

 rudder being still below the keel), to frustrate the one- 

 sided flow behind the stem, and do away with the con- 

 sequent turning force. Of these three kinds of remedy 

 the last-named proved much the most effective, proved 

 indeed an almost perfect cure, thereby confirming the 

 surmise that the one-sided flow at the stern was the chief 

 source of the evil. A minor modification of this dead-wood, 

 with the rudder in its proper place, such as could be 

 practically applied in the ship, likewise proved very toler- 

 ably effective, the average helm angle required' being 

 reduced to one-third of its amount. 



On the strength of the results of these experiments, the 

 Admiralty added a structure of this kind to the stern of the 

 ship, with a result which, while it was a remarkable corro- 



boration of the model experiments, was also on the whole 

 a decided ^success from a practical point of view, the 

 reduction eff"ected in angle of helm being quite sufficient 

 to qualify the ship to steam at full speed in a squadron 

 and keep station satisfactorily. 



B" 



EDWARD T. HARDMAN. 

 Y the unexpected death of this geologist, on the 30th 

 ult, Irish Science has been deprived of one of her 

 most promising followers. Mr. Hardman was born in 

 Drogheda in 1845, and distinguished himself by the posi- 

 tion he took at the Grammar School there, gaining a 

 Government Exhibition and an entrance to the Royal 

 College of Science in Dublin. He soon displayed his 

 strong natural bent towards scientific pursuits, and when 

 he quitted the College he had gained its diploma of 

 Associate and taken a prominent place among its fore- 

 most students, more particularly in the departments of 

 chemistry and geology. In 1870 he was appointed to the 

 Geological Survey, and threw himself with characteristic 

 ardour into the prosecution of field-work, while his know- 

 ledge of chemistry and mineralogy led to his being em- 

 ployed in special services where this knowledge was 

 made available in the work of the Survey. His reports 

 on the Tyrone and Kilkenny coal-fields are good examples 

 of the extent of his knowledge and of his powers of 

 literary expression. He also made his mark by the 

 publication of papers outside the limits of official work. 

 His interesting and suggestive memoir on the origin of 

 Lough Neagh and his papers on anthracite and chert are 

 well known. 



In 1883 the Government of Western Australia applied 

 to the Colonial Office for the services of a trained geo- 

 logist to examine and report on the mineral resources 

 and geological structure of the colony. Mr. Hardman 

 was selected for the post, and obtained leave of absence 

 from the Home Government to enable him to undertake 

 the duties. He was absent upwards of two years, during 

 which time he effected a preliminary survey of a wide 

 tract of unexplored country, and made known its geo- 

 logical structure. In particular, he indicated the presence 

 of gold, and pointed out the areas where gold-fields might 

 be looked for. After enduring great hardships in the 

 bush, he returned to this country, and resumed his duties 

 in the Geological Survey. But the exposure in the 

 Australian climate seems to have told upon his health. 

 He had not been quite well during the spring, and at last 

 he rapidly fell a victim to an attack of typhoid fever. We 

 understand that arrangements had been nearly completed 

 for recalling him permanently to take charge of the 

 mineral surveys of Western Australia, when his sudden 

 death occurred. He has left a widow and two children 

 with no adequate provision, and his friends have already 

 begun to take steps for collecting subscriptions for their 

 behoof. Prof. V. Ball, of the Science and Art Museum, 

 Dubhn, and Dr. Henry Woodward, of the Natural 

 History Department of the British Museum, Cromwell 

 Road, S.W., have kindly undertaken to receive subscrip- 

 tions. 



NOTES. 

 The Natural History branch of the British Museum in Crom- 

 well Road has just received a most important donation from 

 Lord Walsingham, consisting of a collection of Lepidoptera 

 with their larvse, mainly British butterflies {Rhopalocera) and 

 certain families of moths {Heterocera), including Sphingidce, 

 Bombyces, Pseudobombyces, Noctua;, Geomctridir, and Pyralidce. 

 There is also a fine series of Indian species, collected and pre- 

 served at Dharmsala, in the Punjab, by the Rev. John H. 

 Hocking, and specimens of exotic silk-producing Bombyces in 



