22 



XATURE 



[November i, i8q4 



proper motion a term /i' has to be added to P, the value 

 of which tends to o"'4S as the magnitude, and the proper 

 motion increases. So long ago as 1S72, Prof. Gylden 

 showed that it is justifiable to deduce the distance of a group of 

 stars from their apparent mean brightness in all cases « here the 

 probability of a certain inlensily of illuminating power is a 

 function of this intensity alone, without depending upon position 

 in space. And since the photometric law has been proved to 

 be at least approximately valid in this case, it may be concluded 

 that the brightnesses of stars reduced to the same distance are the 

 same, on an average, for all distances which can enter into our 

 consideration. But the most important result of the present 

 investigation is the determination of the mean parallax of first 

 magnitude stars reduced to the zero of apparent motion. The 

 value for this, which is o" 204, may he considered as identical 

 with Peters's value of o" '209, especially when it is borne in mind 

 that the latter value is not reduced to zero apparent motion. 



THE INSTITUTION OF MECHANICAL 

 ENGINEERS. 

 C\^ Wednesday and Thursday evenings of last week, October 

 ^-^ 34 and 25, a general meeting of the Institution of 

 Mechanical Engineers was held at 25 Great George Street ; 

 the President, Prof. Alexander B. \V. Kennedy, occupying the 

 chair. The two following papers were read and discussed : 



" The Manufacture of Standard Screws for Machine-made 

 Watches," by Mr. Charles J. Hewitt, of Prescot. 



"Drilling Machines for Cylindrical Boiler Shells," by Mr. 

 Samuel Dixon, of Manchester. 



Mr. Hewitt's paper was of an interesting nature. He is the 

 works manager and chief mechanic of the Lancashire Watch 

 Factory, an establishment recently started at Prescot for the 

 manufacture of watches on a large scale in one works. The 

 factory system of watch production has been, as is well known, 

 carried to a very successful issue in the United States, where 

 the Elgin and Waltham Watch Companies annually make large 

 numbers of excellent lime-pieces wholly by machinery. .\s, m 

 all cases, where highly skilled hand labour, performing intricate 

 operations, is superseded by mechanical appliances, the ma- 

 chines used are of a h'ghly orgmised and costly nature. In the 

 case of the minute parts required in watch-making, this feature 

 is very strikingly emphasised. Perhaps some of our readers may 

 remember the exquisite little machine tools exhibited by the 

 Waltham Watch Company, at the Inventions Exhibition, 

 in the year 1SS5. These were a revelation to most English 

 watchmakers, accustomed to the small factories and per- 

 fectly rude appliances of the British industry, in which the 

 highest skill of the operators, due to special trainin; from 

 earliest youth, compensated tor the lack ol ingenuity displayed 

 in the construction of the tools used. In the case of 

 watches, as with so many other mechanical productions, the 

 brain capital expended in the employment of construction 

 of machines bears fruitful interest in the shape of less 

 skilled labour required in their use. The same thing may 

 be observed throughout the whole range of mechanical in- 

 dustry. The file, the hammer, and chisel are the primi- 

 tive tools of the engineer, requiring simple inventive power 

 in their inception, but great skill in their use. The planing 

 machine, by which the same end is obtained mecha- 

 nically, of producing a flat surface, as was got originally 

 by chipping and filing, required kno>vlcdge and skill for its pro- 

 duction, but a comparatively small amount of those qualities lor 

 its operation. The same thing is true, even to a greater extent, 

 in the case of the still more modern machine tool, the milling 

 machine, which is often attended by boys, possessing no 

 mechanical knowledge whatever, during its production of 

 finished lorms such as would have required a highly skilled 

 workman in former days. 



The heaulilul machines referred to by the author in his paper, 

 examples of which »ere sho'ii at the niccungs, carry the 

 same principle many steps farther. As was remarked, the 

 machine shown for making wach-screws may lie said to stand 

 in the same relation to oidmary engineers' machine tools as 

 cosily gems to common building stones. 



.Mr. Hewitt commenced his description by dwelling upon the 

 difficulties experienced by wal hiiiakcrs in old times, when 

 there was no general siandaid lor dimensions and pitch ol 

 screws, or lorm ol thread. Su h was necessarily the case with 

 hand-woik, but a machine can lie depended upon to turn out 



NO. 1305, VOL. 51] 



many thousands of parts exactly similar, so that a screw could 

 be put into a watch made years previously. The advantage, 

 naturally, is most apparent in the case of repairs and renewals. 

 Thestandardofscrewsadopled by the Lancashire Watch Company 

 at their Prescot Works, is that recommended by the committee 

 of the British .•Vssociation, and described in the report of 1S82. 

 It is a V.thread of 47); degrees, rounded top and bottom through 

 I'l of the height, and the pitch is directly related to the 

 diameter of the formula D = 6P' . In arranging the standard 

 the first business was to make master taps, which were pro- 

 duced on a small screw-cutting lathe specially designed for the 

 work, and having a corrected screw, accurate within very close 

 limits. Taps being thus produced, screw-dies were made to the 

 exact standard. When cut the thread requires hardening, and 

 this causes some amount of distortion, which is corrected by 

 grinding the threads with a soft steel lap charged with diamond 

 dust, the operation being performed in the same lathe that cuts 

 the thread. The die used is simply a tapped hole in the centre 

 of a small thin disc of steel, it being an object to have as little 

 metal as possible surrounding the hole, so as to reduce the dis- 

 tortion produced by hardening. Although the die is not split, 

 the pressure exerted by the die-holder is sulTicienl to produce a 

 slight modification in the diameter of the screw, and in this way 

 the alteration caused by hardening is corrected. During the 

 discussion this fact was questioned, but Mr. Hewitt says that 

 the statement is absolutely correct. The machine itself is of 

 an intricate design, as may be imagined when it is stated that 

 perfect screws are turned out automatically from the plain rod 

 or wire. There are four hollow spindles through which this 

 wire is fed forward to the operating tools, which are four in 

 number, and are carried on a revolving turret. There is also 

 a further tool for making the slit in the screw-heail for the 

 turn-screw. It would be useless to attempt to describe the 

 mechanism of this very ingenious lathe without the aid of 

 elaborate drawings. Indeed, during the discussion several 

 engineers, well skilled in mechanical appliances, confessed 

 themselves unable to follow the train of mechanism, even with 

 the aid of working drawings elisplayed on the walls of the 

 theatre. It is enough to say that the m.ichine will go on 

 without any attention so long as the wire to form the screw 

 lasts, when it slops of itself. 



.■\. short discussion followed the reading of the paper, but no 

 fresh points were raised ; the speakers, for the most pari, con- 

 tenting themselves with complimenting the author on the 

 ingenuity of his tlesign. 



On ihe second evening of the meeting, Mr. Dixon's paper, on 

 drilling machines lor boiler shells, was read and discussed. The 

 introJuclion of sieel as a material for steam-boiler construction 

 opened up a new era in that branch ol industry. When iron 

 plates only were used, a first-class b lilcr-shop possessed, as the 

 chief part of iis plant, simply a punching machine and a pair 

 of rolls for bending the plates ; the rest «.as done by handwork, 

 and that of a bignly skilled nature. Now that machinery has 

 superseded the handicraftsman, rivetling is done by most costly 

 and beautifully dc-igned hydiaulic apparatus, necessitating in 

 Us invcniioii a knowledge of applied science ol a nigh order. 

 Hanging ol the immense boiler-plates ol the present day is also 

 effected by heavy hydraulic presses. The rolls now used for 

 l)ending plaies have to be de^igned on true mechanical principles, 

 whilst great advance has been made in drilling inacfiincry. 'I'hus 

 tioifi ill the enormous boilers of our large steam hips and in the 

 iliniiiuitive mechanism ol watches, we see the skilled handi- 

 craltsmaii being displaced by automaiic macninery. It was 

 soon found impossible to make steel boilers with the same plant 

 that was used for the old type of iron boilers ; the 

 difference in the physical properties of the material 

 ahmc demanded a change in treatuiirnt. The soUer and less 

 homogeneous n on enabled the nvel-holes to be punched, but it 

 was found that this work done upon steel pbtes caused a 

 deterioration of the metal ; diilling, thereine, h.ad to be sub- 

 stliuied lor punching. Iron plates were punched in the Hat; 

 but It was lound that with steel when the holes were made in 

 th.it way, they often would not go together accurately so as to 

 take ihe rivets 10 ii.c greatest advantage, ihe lesuh being a weak 

 joint. '1 his did not mailer so much wlien steam pre>sures were 

 low, but Willi the greater demands male uy ihc marine 

 engineer in proilucing motive power ccunoinic dly, higher 

 prts.ures liad to be used, and there was no nia'gui lor loss in 

 ihc line of livening. It therefore became cusmmury to bend 

 the plates and put ihem in;o shape to form the shell ol the 



