April 13, 191 1] 



NATURE 



227 



■down of part of the machinery. There must also be a 

 prospect of a reasonable cost of upkeep. Leaving warships 

 out of account, oil fuel is only used on shipboard in those 

 cases where the natural advantages render its use more 

 economical than coal, and by vessels which trade regularly 

 to ports where supplies can be obtained. For the ordinary 

 •cargo steamer which has to seek employment all over the 

 globe, coal is still the necessary fuel. 



The Diesel engine for marine purposes is made in three 

 forms, viz., as a four-stroke cycle single-acting engine, a 

 two-stroke cycle single-acting engine, and a two-stroke 

 ( \cle double-acting engine. An auxiliary air compressor 

 < ;ipable of producing a pressure of about yoolb. per square 

 inch is required. The author has examined the turning 

 moment diagrams of different arrangements of cylinderSj 

 and shows that a four-stroke cycle engine with twelve 

 cylinders, a two-stroke with six cylinders, and a double- 

 acting with three cylinders give fairly uniform Forsion 

 moments, the ratio of maximum to mean being not greater 

 than I'l.v With these numbers of cylinders there is 

 nothing further to be desired regarding steadiness of 

 motion. The Diesel marine engine should be Diesel only 

 as regards the cylinders and their accessories, and should 

 be of the ordinary marine type as regards all the rest of 

 the engine. The question of the auxiliary machinery 

 n quired is fully discussed in the paper. 



Dr. Diesel stated in the discussion that any kind of oil 

 may now be used in these engijies, and that the use of 

 ilie two-stroke cycle may be assumed in future for marine 

 purposes. Some 250 vessels are now fitted or to be fitted 

 with Diesel engines, a large number of these being sub- 

 marines. The use of Diesel engines in submarines has so 

 extended their radius ot action as no longer to limit their 

 use for coast defence merely. About 1000 horse-power is 

 the largest power obtained from one cylinder up to the 

 present, the cylinder being of the two-stroke double-acting 

 type. Some makers are prepared to give higher powers 

 fiom one cylinder. 



Messrs. Richardson, Westgarth and Co., of Middles- 

 ough, are now constructing a set of single-screw Diesel 

 igines of 1000 horse-power for a 3200-ton ship to the 

 .'ider of Lord Furness. These will be of slow-running type. 

 The Anglo-Saxon Petroleum Co. have on order a single- 

 screw vessel of 4250 tons to be fitted with iioo horse-power 

 I )ifsel engines, to be built by an Amsterdam firm. 



Considerations affecting local strength calculations form 



the subject of a paper by Mr. J. Montgomerie. It is a 



iruism that there is no such thing in the calculations 



flraling with the strength of ships as an actual quantitative 



-tress in tons per square inch. " To design a ship from 



first principles " is a phrase which is often used in a sense 



implying far too much. All calculations of the strength of 



-hips are comparative. Structural arrangements of vessels 



!iich ha.ve stood the test of experience are taken, and are 



iinparcd and contrasted with those proposed in any given 



-e, or a corresponding arrangement is derived from them 



!iich shall be satisfactory in the case being dealt with. It 



- of importance to eliminate, so far as possible, errors 



Iving at the root of the comparison. For example, the 



iimparison of a beam of symmetrical section with another 



unsymmctrical section by use of the ordinary beam 



1 mulrt- may produce very large errors. Again, errors 



ten arise through want of proper consideration in cases 



\ combined normal and shearing stresses. The effect of 



lered flexibility in a proposed arrangement often causes 



1 entire change in the basis of comparison, and is generally 



nifcirmly neglected. Recent experimental work by Lilly 



1 columns and Bach on flat plates was referred to. In 



uinection with the latter subject comparatively little is 



lown experimentally for rectangular plates fixed at the 



ii:;es, and Dr. Thearle announced that the committee of 



lovd's Register had made a pecuniary grant to the author 



the paper to assist in enabling further experiments to be 



irried out. 



The acceleration in front of a propeller is the subject of 

 a paper, in whith Dr. R. E. Froude resists the inroad 

 which a propulsion paper read by Prof. Henderson last 

 year makes upon Dr. Froude's paper of 1889. The prin- 

 cipal purpose of the latter was to prove from hydro- 

 dynamic theory that, in so far as the fluid acceleration bv 

 which thrust is satisfied may be treated as external to the 

 ropeller, one-half of that acceleration must take place 



NO. 2163, VOL. 86] 



before the propeller in obedience to defect of pressure in 

 front of it, and the other half after it, in obedience to 

 excess of pressure behind it. Prof. Henderson's paper of 

 last year purports to prove, also from theory, that the 

 precedent acceleration cannot possibly contribute to thrust. 

 In the present paper Dr. Froude reasserts his theory, 

 together with such further considerations as appear to be 

 called for by Prof. Henderson's paper. 



Herr H. Frahm contributes a paper giving the results of 

 trials at sea of his anti-rolling tanks. Reference has 

 already been made to Frahm 's arrangement in Natltre. 

 When in full action, the tanks on the ss. Ypiranga and 

 Corcovado exert a turning moment of 2790 foot-tons, thus 

 counteracting wave impulses of equal turning moment. In 

 order to obtain equal efficiency in damping out rolling, the 

 same turning moment ought also to be exerted by any other 

 anti-rolling device, such as a gyroscope, which might be 

 fitted to these ships. It is doubtful if it will be possible 

 to develop the gyroscope sufficiently. The ss. General 

 (13,620 tons loaded displacement), of the German East 

 African line, started on her maiden trip at the beginning 

 of March. When crossing the Bay of Biscay, she encoun- 

 tered a storm which made her roll 14° on either side when 

 the tanks were out of action. This was reduced by 7° or 

 8° when the small fore tank was put into action, and with 

 both tanks in action, the rolling was reduced to 3° in 

 either direction. A large working model was shown in the 

 library of the Royal Society of Arts. The ship was set 

 rolling in a tank by means of an electromotor, operating on 

 the model by means of a very flexible flat spring. The 

 model showed very clearly the efficiency of Frahm 's tanks 

 in reducing rolling. 



Prof. E. G. Coker describes his optical method of in- 

 vestigating stress in plates of variable sections, and gives 

 some applications to ship's plating. The method has been 

 already noted in Nature, and it may be now added that 

 the author has developed a method of obtaining the 

 stresses quantitatively. This may be done by subjecting a 

 standard test-piece to such a degree of pull or push that 

 the colour produced agrees with that at a desired point in 

 the body under examination. Or by a method modified so 

 as to get rid of the necessary judgment in matching colours ; 

 this modified method may be used in all cases of pull or 

 push stresses, and consists in arranging a simple pull or 

 push member in the same field of view as, and immediatelv 

 in front of, the object under examination. To determine 

 the stress at any point, the reference member is loaded 

 until the original dark field produced by the optical arrange- 

 ment reappears. When this happens, the stress in the 

 reference member is the same as that at the point con- 

 sidered, and no correction is required for the alteration in 

 thickness produced bv the stress, since both test pieces are 

 in exactly the same condition. 



STATE SURVEYS."- 



PHE true economy of executing land measurement of 

 -'■ the highest precision as a control upon more detailed 

 work, which can then be done more quickly and at less 

 cost, is now generally admitted, and wherever the area is 

 large such control work is carried out by a central adminis- 

 tration for the use and assistance of local surveys. 

 Methods will vary in different areas and with the special 

 object in view, but such coordinated work on a large 

 scale has great advantages over small scattered areas in 

 which work is carried on independently. 



(i) The operations of the Survey of India during the 

 twelvemonth ending September 30, 1909, are described in the 

 report which has just been issued. Primary triangulation 

 was carried on in Beluchistan, Kashmir, and Burma over 

 an area of 9600 square miles, besides a certain amount of 

 building and selecting station ; the average triangular of 

 three groups completed were 0'4i*, o-6*, and 0-47*. The 

 lo-foot standard bar A having returned from .Sevres, 

 whither it had been sent in 1908 for comparison with the 

 international metre, was recompared with the secondaty 

 standard bar of the Survey, and the results show that it is 



1 (i) "General Report on the operations of the Survey of India." By 

 Col. F. B. I,on(?e, R.K. (Calcutt.^, 1910.) 



(i) United .States Geological Survey, Washington. Bulletins 434, 437. 

 Spirit Levelling, i8q6 to tqoq. 



Bulletin 440. Results of Triangulation and Primary Traverse, 1906-S. 



