September 26, 1884.] 



SCIENCE. 



323 



ing the progress of their work from scientific stand- 

 points. Besides appointing a committee of invitation 

 to increase the interest and attendance for the next 

 meeting, two special committees were appointed to 

 work np the subjects, ' The best method of teaching 

 mechanical engineering,' and 'The use and value of 

 accurate standards, screws, surfaces, gauges, etc., and 

 of systematic drawings, in the modern machine-shop.' 

 On Friday, Mr. J. C. Hoadley read by request his 

 excellent resume of steam-engine practice in the 

 United States; reviewing the different classes of en- 

 gines, and giving figures to show their economy, with 

 other important facts. Mr. Hoadley classifies engines 

 as follows: large compound engines for pumping, 

 etc., rolling-mill engines, saw-mill engines, marine 

 engines, locomotives, hoisting-engines, steam-cranes, 

 steam-pumps, portable engines, etc., and engines for 

 electric lighting. This would seem to be an enu- 

 meration, rather than a classification, of different 

 types of engines. The paper contains, in compact 

 form, information as to all the prominent engines, 

 and forms a valuable addition to steam-engine litera- 

 ture. It will be printed in full in the Transactions. 



The subject for the day was then introduced by a 

 paper on the training for mechanical engineers, by 

 Prof. G-. I. Alden of Worcester, Mass., in which one 

 phase of the subject was presented. Professor Alden 

 urged the importance of practical as well as scientific 

 attainments, and claimed that the shop for manual 

 instruction should not be such an institution as would 

 he developed by or out of the school, but should bring 

 with it not only the methods but the business of an 

 actual productive machine-shop, the work being done 

 for the market. It is to be regretted that other promi- 

 nent gentlemen expected to furnish papers were pre- 

 vented from attending. 



The discussion commenced with so much interest, 

 that an extra session was devoted to it, when the 

 various phases of the question were brought out. A 

 starting-point was thus formed which should enable 

 the committee to secure a more complete, important, 

 and decisive discussion next year. Messrs. Rigg, 

 Kent, etc., and Professors Woodward, Robinson, 

 Wood, Thompson, Higgins, Carr, etc., and Webb, 

 joined in the discussion; and the latter called at- 

 tention to the necessity of distinguishing between 

 machine-shop practice and experiments in the me- 

 chanical laboratory, and pointed out three existing 

 and natural kinds of schools : 1°. manual training 

 schools, where the manual exercises are for discip- 

 line only; 2°. schools for master-machinists, superin- 

 tendents, etc., as at Chalons-sur-Marne, where the 

 course is seven hours daily, for three years, in the 

 shop, with such instruction in mathematics, draught- 

 ing, etc., as can be added thereto; 3°. schools for 

 mechanical engineers (as the Ecole centrale), where 

 theoretical training predominates, and where there is 

 either no shop-practice, or only such as is specialized 

 and organized so as to give, in the limited time avail- 

 able, the maximum intellectual and manual grasp of 

 machine-shop methods. 



On Monday Prof. W. A. Rogers read a paper on a 

 new method of producing screws of standard length 



and uniform pitch; and Mr. J. A. Brashear, a paper 

 on the production of optical surfaces: the subject 

 for the day being the value of accurate screws, sur- 

 faces, etc., in the machine-shop. Professor Rogers 

 has developed a method by which practically perfect 

 screws can be cheaply made, and Mr. Brashear has 

 succeeded in making perfectly flat surfaces of larger 

 size than usual. Professor Rogers's method of mak- 

 ing a screw presupposes a correctly graduated scale 

 over which a microscope attached to the lathe-carriage 

 moves. The error in the movement of the carriage 

 is thus made visible, and can be neutralized by means 

 of a stout micrometer screw, which varies slightly the 

 position of the cutting-tool on the carriage. By this 

 means the screw is cut so nearly true that the remain- 

 ing inequalities are easily ground out by means of a 

 long nut cut into four pieces, which can be put to- 

 gether in different ways so as to make the errors in 

 the nut oppose those of the screw. Professor Rogers 

 pointed out the way for further improvements, and 

 hoped that some way would be found for the detec- 

 tion of errors extending over long distances, by means 

 of gratings ruled by the screw. The subject of the 

 proper use and preservation of such perfect screws in 

 the machine-shop was also touched upon by Mr. 

 Pickering, who has found means in his own practice 

 of distributing the work as equally as possible over 

 the whole leading screw of a lathe in order to keep it 

 from wearing unequally. This whole subject will 

 come up next year for discussion, and the paper was 

 deemed of such importance as to warrant its publica- 

 tion in full in the Transactions. Mr. Brashear's paper 

 is also to appear in, full. The discussion of these 

 papers, engaged in by many prominent physicists and 

 engineers, was highly interesting. It opened by a 

 criticism from one of our English friends, who ex- 

 pected to find every thing in the United States done 

 by machinery, and was disappointed to find that these 

 flat surfaces (or slightly curved, when needed so for 

 lenses, etc.) were produced by polishing, much in the 

 old manner; and it was claimed that the correct form 

 should first be produced by machinery, and the polish 

 put on subsequently. The telescope of Mr. Bessemer 

 was alluded to as an instance where such work would 

 be done by machinery. Several gentlemen followed, 

 and spoke of the difference between ordinary work 

 which might thus be produced, and the extremely ac- 

 curate forms required for astronomical purposes pro- 

 duced by Mr. Bessemer. Professor Harkness described 

 his measurements of the 'transit of Venus' plane 

 mirrors down to hundred-thousandths of an inch, and 

 showed that work was done in the United States to a 

 degree of accuracy not perhaps appreciated in Europe. 

 Mr. Brashear closed the discussion by a complete de- 

 fence of his methods. He claimed that the degree of 

 accuracy of his work was such, that, after a surface 

 was polished, he could, by a few suitably lengthened 

 strokes of the polisher, make it parabolic, elliptic, 

 or any thing he wished, and that his principal diffi- 

 culty was that the finest polishing powders cut too 

 fast, so that to shape first and polish afterward was 

 meaningless: then, growing eloquent, he ventured, 

 for reasons which he explained, to predict that Mr. 



