March 14, 1895 J 



NATURE 



^75 



each case all the experiments have been successful, and on one 

 occasion only were we troubled by a disturbance due to a 

 note (of about 253 vibrations) when sounded alone. A slight 

 readjustment of the cone, however, eliminated this effect 

 entirely. 



Suih difficulties make it no easy matter to set up 1 he apparatus 

 in a huiry, and the most I can hope to do this evening is to 

 demonstrate to you the methods of u^ing i^ I cannot under- 

 take to make the actual measuiements before you. 



It is, however, desirable 10 illustrate the sensitiveness of the 

 apparatus to vibrations of 64 per second, and its insensitiveness 

 to other sounds. 



Provided the current of air does not travel directly down the 

 cone, organ-pipes may be blown just outside it without pro- 

 ducing any etTect. One of Konig's large tuning-forks may be 

 bowed stroni;ly without effect. 



If, however, the exciting fork be tuned to 64 vibrations per 

 second, and if it be struck as lightly as possible with the 

 handle of a small gimlet, used as a hammer, the handle having 

 been previou>ly covered with india-ruiiber, the bands will 

 immediately vanish, though the note produced is often quite 

 inaudible, even to a person whose ear is placed close to the 

 fork. 



Let the weights on the fork be shifted so that it makes 

 63 5 vibrations per second, then the resonating fork beats, and 

 the bands regularly appear and disappear every two seconds. 



Having thus explained the construction and working of the 

 apparatus, let me show you how we have tested wheiher it 

 responds to a difference tone. When the proper rows of holes 

 are opened, the siren will give simultaneously the c of 256 and 

 the e of 320 vibrations. The interval is a major third, the 

 diflference tone is 64 vibrations. The pitch is determined by 

 the beats between the upper note and a standard tuning-fork 

 which gives e . Sounding the upper note al me no effect is pro- 

 duced on the interference bands, as the beats first appear, then 

 die out, and are finally heard again when the note given by the 

 siren is too high. 



It could be shown in like manner that the 256 note alone 

 produces no effec', but if, when the standard fork of 320 

 vibrations and the upper note of the siren are judged to be in 

 exact accord, the 256 note be also produced, the bands im- 

 mediately disappear. Sometimes, of course, a small error is 

 made in the estimate of the pitch, and the effect is not instant- 

 aneous, but in every case the bands disappear when the beats 

 between the two notes are so slow that they cannot be 

 distinguished. 



It is therefore evident that Helmholtz was right when he 

 asserted that the ditference tone given by the siren is objective. 

 It exists outside the ear, for it can move a tuning-fork. 



( To be continued. ) 



JAMES WATT AND OCEAN NAVIGATION.^ 



TF it be asked what James Watt did during his long, busy, 

 and eventful life to improve ocean navigation, or to adapt 

 the steam en;;ine to the work of propelling ships, I am obliged 

 to reply that I am not aware he personally did anything, or even 

 that he concerned himself much about the matter. He took no 

 active part that we know of in applying or adapting his steam 

 engine to the \ ropulsion of ships. Tne reason probably was 

 that after his attention wa-; first directed to the subject of the 

 steam engine, or (ire engine, in 1759, his whole energy 

 was expended, first in improving the steam engine and 

 making its manufacture commercially successful, and afterwards 

 in executing ihe rrders that came for pumping and other engines 

 that were required for mines and manufactures. In the case of 

 most of the greatest mechanical inventions — -Watt's among the 

 number — it has not been the ideas or the inventions by them- 

 selves that have brought success, prospC'ity, or even satisfaction 

 to their owners. These results have had to be p.ainfully and 

 slowly evolved out of long and costly practical demon trations 

 and experience of the alleged merits of the invention, fames 

 Walt toiled, suffered ami endured for more than twenty years 

 after his discovery of separate condensation in 1765, before he 

 could see that his steam engine would ever bring him anything 



' Abslr.icl of the Watt Lecture, delivered by Dr. Francis Elg.->r at 

 Greenock, on Janu.-iry j8. 



NO. 1324, VOL. 51] 



but disappointment, Io?s, and misery. It is highly characti ristic, 

 however, of Watt's ferule and original genius, and significant 

 of what he might have done to develop the marine engine at 

 the commenceiiicnt of its history, had he taken the mat'er up, 

 that upon Ihe two principal occasions we know of when he 

 applied his mind to the subject, he made very pregnant sug- 

 ge-tions. Thus, when Wait sent drawings of his engines to 

 Soho in 1770 for Mr. Bnu'ton to construct one for experiment, 

 and had been told that it was intended to make an entice to 

 draw canal boats. Watt wrote, " Have you ever considered a 

 spiral oar for that purpofe, or are you f>rtwo wheels? "and to 

 make his meaning clear he sketched a rough but graphic outline 

 of a screw propeller. This is, perhaps, the earliest suggestion of 

 a screw propeller, except that it was proposed by Daniel 

 Brrnoulli, 'he mathema'ician, in 1752. Again, in 1816, four 

 years after the first Clyde steamboat, the Comet, was built at 

 Port Glasgow, when Mr. Watt was upon his last visit to 

 Greenock, he went to Rothesay and back in a steamboat. W 

 that time the engineer did not reverse his engines, but merely 

 stopped them some time before the vessel reached hermooring- 

 place, and let her gradual'y slow down. James Watt, then an 

 old man of eighty, tackled the engineer of the boat, and showed 

 him how the engine could he rever-ed. He tried to explain 

 this with the aid of a foot rule, but not being successful in doing 

 it to the compl. te satisfaction of the engineer, he is said to have 

 thrown olT his overcoat and given a ( ractical demonstration. 

 Although Watt never took up the subject of s earn navigation 

 and never made a marine engine, still he was in reality its 

 originator, because he discovered and provided the means by 

 which it could be applied with advantage to the propulsion of 

 ships. Each of his great improvements upon the old engine 

 that worked by atmospheric pressitre and condensed its steam 

 in the cylinder — such as the separate condenser, the working 

 by steam pressure as well as by pressure obtained by vacuum, the 

 double action of the steam in the cylinder on both sides of the 

 piston, working the steam expansively, the centrifugal governor 

 for automatically regulating the speed of the engine, and 

 many others — was a direct adaptation for marine purposes. 

 There is one point in the history of shipping at which we 

 can draw a definite line between old and new when changes 

 were made so radical in the.r nature, and so rapid .and universal 

 in their operations, that all which came after is fundamentally 

 different from what existed before. The period of transition 

 falls in the early part of the present century, when the propul- 

 sion of ships by steam power was substituted for propulsion by 

 the wind — the motive power that h.id been employed from time 

 immemorial — and when the material out of which their hulls 

 were built was changed from wood to iron. The late- 

 ness of this period and its near proximity to the present, 

 is illustrated by the fact that it was not till after the 

 accession of H.M. Queen Victoria that steamships and ships 

 built of iron came to be regularly employed in ocean navigation. 

 At the close of the first third of the nineteenth century, the 

 over sea trade of the world was carried on with ships that were 

 all built of wood and propelled by sails. Only about 200 of 

 these were over 500 tons in burden, or much over 100 feet long. 

 Nothing approaching to such a rapid and complete revolution 

 as these two great changes brought about in the dimensions, 

 forms, and all the characteristics and qualities of ships, in the 

 conditions of life on board ship, and in travelling by sea, was 

 ever experienced before in the known history of shipping. All 

 the old ships of which we h.ave any knowledge — .and by old 

 ships I mean .all that existed prior to the introduction of steam 

 — were built and fashioned entirely by manual power, 

 with the aid of very simple tools ; and they were either pro- 

 pelled through the water by manual labour, or by sails that 

 could be worked in the simplest manner by the crew. One of 

 the broadest distinctions between the ships of the past that were 

 built of wood and propelled by sails and those of the present 

 that are built of iron or steel and propelled by steam, is that 

 everything had to be done in the former by the hand of man, 

 without any aid from machine tools or other modern Labour- 

 saving and labour-helping appliances. .\nd this was so both 

 in preparing the materials used in building the hull and shaping 

 them to their requisite form, putting them in position, r.istening 

 them together, and in working the ship at sea and handling the 

 sails so as to make the pressure of the wind most eflective for 

 propulsion. In modern ships, almost everything is, on the 

 other hand, done by steam-power in its various applications. It is 

 by this means the plates which form the hull are first of all rolled 



