l82 



NATURE 



[June 25, 1891 



difficulty in generating higher pressure steam caused 

 stagnation in marine engineering practice ; until the sub- 

 stitution of steel for iron in boiler making, the advent 

 of new types of furnaces, and improvements in the 

 machinery used in boiler construction have enabled 

 pressures as high as from 150 pounds to even 200 pounds 

 to the square inch to be carried. The result has been 

 that, for the two-cylinder compound engine, there have 

 been substituted two types of engine, known respectively 

 as the triple expansion engine and the quadruple expan- 

 sion engine. The names are misleading, as even the 

 ordinary compound engine expands its steam more than 

 three or four times. 



The growth of the science of marine engine design, 

 which we have so briefly sketched out, may appear, to 

 those who are not engineers, but little more than a record 

 of increasing steam pressures. Undoubtedly a higher 

 steam pressure has been the fundamental reason for these 

 advances, but the carrying out of these successive changes 

 in pressure has necessitated an entire reconstruction of 

 marine engine practice ; so that an engine working at 1 5 

 pounds pressure can hardly be said to belong to the same 

 category as one working at 150 to 200 pounds pressure. 

 Tooth-wheel gearing, which was first used with screw 

 propellers, has long ago disappeared, side levers and 

 trunks are no longer introduced, and the surface conden- 

 ser has become a necessity. In the old days, with jet con- 

 densers, the boilers were fed entirely with salt water, now 

 in the best marine practice the condensed steam is all 

 returned to the boiler, excepting that which is unavoidably 

 lost, and this quantity is made up by special distillers and 

 condensers, the manufacture of which has introduced a 

 new branch of marine engineering, as may be judged by 

 several exhibits by different firms in the Exhibition. The 

 practice of circulation of refrigerating water through the 

 surface condenser by means of separate centrifugal pump- 

 ing engines has also introduced a distinctive type of 

 auxiliary marine engine, upon which several important 

 firms have been chiefly employed. Indeed, the increase 

 in auxiliary machinery has been as marked a feature in 

 the recent progress of marine engineering as have been 

 the changes in the main engines themselves. A battle- 

 ship of the first class will carry between seventy and eighty 

 separate engines, in addition to those used for driving the 

 propellers. These include electric light engines, hydrau- 

 lic machinery in connection with the working of heavy 

 guns, steering engines, &c. As an instance of what is 

 gained by the use of auxiliary machinery, an instance 

 given by Mr. White may be quoted- On one occasion it 

 took 78 men \\ minutes to put the helm of the Minotaur 

 hard over. Steam gear was subsequently fitted, by the 

 aid of which two men were able to do the same thing in 

 16 seconds. 



We do not propose to give a list of the various objects 

 exhibited, to which we have referred in penning these 

 remarks. The official catalogue performs that function 

 far more completely than we could hope to do. The 

 collection at Chelsea is well selected and fairly complete, 

 and there will be found there material for object-lessons 

 in all we have advanced in this brief sketch. We may, 

 however, with advantage, add a few figures as to money 

 cost, which cannot fail to be of interest, and for which 

 we are indebted to the Director of Naval Construction. 

 The cost of a i co-gun line-of-battle ship at the begin- 

 ning of the century was about ^65,000 to ;^7o,ooo, arma- 

 ment and stores being excluded. The corresponding 

 outlay on the no-gun sailing three-deckers of 1840 was 

 about ^iiOjOCO ; and that of the 121-gun screw three- 

 deckers of 1859 about ;^230,ooo, machinery included. 

 The Warrior, completed m 1861, cost over ^375,000; 

 and the Minotaur class about ;^48o,ooo. With the in- 

 crease in size of the Dreadnought, and the introduction 

 of hydraulic mechanism, came an increase of cost to 

 ;^620,ooo ; while the Inflexible cost no less than ^810,000." 



NO. I 1 30, VOL. 44] 



The Nile and Trafalgar, zoxapXeie with armament, would 

 represent little less than a million sterling each. The 

 cost of the armour-plating, propelling machinery, and 

 hydraulic gun mountings alone, would have paid for five 

 first-rates of Nelson's time. The sum paid for the 

 armour alone on one of our latest battleships, such as 

 the Royal Sovereign, would pay for the Natural History 

 Museum at South Kensington ; whilst even a first-class 

 torpedo-boat costs as much to build and equip as a 40- 

 gun frigate of N elson's time. 



A GEOLOGICAL EXCURSION IN AMERICA. 

 T BEG to call to your attention the following short 

 •*• account of a geological excursion planned for the 

 benefit of foreign geologists who may attend the coming 

 meeting of the International Geological Congress in this 

 city in August next. It will afford an exceptionally 

 favourable opportunity for European geologists to become 

 personally familiar with the most important geological 

 phenomena of the United States. 



I venture, therefore, in their interest, to request that 

 you publish some notice of it in your widely circulated 

 periodical, with a request that those who desire to take 

 part in it will kindly advise me as early as possible, in 

 order that arrangements may be thoroughly perfected 

 beforehand. A single train will carry 75 to 100 persons 

 comfortably. If more join, the party will be arranged in 

 two trains. Arrangements will have to be made before- 

 hand at the various stopping places along the road for 

 the reception of the party, and you can therefore readily 

 understand the importance of knowing as early as pos- 

 sible how many are to be accommodated. 



S. F. Emmons, Secretary. 



Washington, D.C., May 30. 



.For the close of the fifth session of the International 

 Congress of Geologists, which is to be held at Washing- 

 ton, D.C., from August 26 to September 2, a grand geo- 

 logical excursion has been organized, which presents 

 unusual attractions and facilities for the European geo- 

 logists who attend the Congress, and who wish to see 

 some of the geological w^onders which have become 

 familiar to them through the memoirs of American 

 geologists. The excursionists will start from Washing- 

 ton, on September 3, on a special train of Pullman ves- 

 tibuled cars, which will constitute a moving hotel, being 

 provided with sleeping and toilet accommodations for 

 both ladies and gentlemen, restaurant cars, smoking, 

 reading, and bath rooms, and barber's shop, and so 

 arranged that travellers can pass freely at all times from 

 car to car through covered passages. It will accompany 

 the party wherever the rails are laid in the regions 

 visited, the hours being arranged so that all the most 

 interesting portions of the route will be passed over in 

 the daytime, and stops may be made wherever any object 

 of special interest to the travellers presents itself. Ame- 

 rican geologists who have made special studies of the 

 different regions visited will accompany the train, and 

 explain their geological structure upon the ground. The 

 main route laid out is over 6000 miles (nearly 10,000 

 kilometres) in length, and extends over 38^ of longitude 

 and 12° of latitude. It is planned to occupy 25 days, 

 and the cost per person will be 265 dollars (1325 francs), 

 which will cover all necessary expenses, of whatever kind, 

 during the trip. 



The following are the principal objects of geological 

 interest which will be seen by those who make the 

 excursion : — 



Going westward, the Appalachian Mountains are first 

 crossed, and an opportunity will be had to see the closely 

 appressed Palaeozoic rocks which constitute their typical 

 structure. The prairie region of Indiana and Illinois, at 

 the southern end of Lake Michigan, its ancient outlet 



