May 15, 1585.] 



♦ KNOWLEDGE ♦ 



407 



constructed to hold only a single pair of dies of the form 

 shown in Fig. 24. An extra piece of metal is usually 

 placed between the dies and the screw to save wear upon 

 the die. The adjusting; screw is placed at the side instead of 

 being used as a handle — the handles being long and rigid, 

 and permitting a considerable amount of force to be 

 applied. 



WHITWORTH TAPS. 



Ex. LIU. — In Fig. 26 is an enlarged illustration of a 

 Wliitworth tap, the threads of which are cut at an angle of 

 55^, rounded at the top and bottom, the curve having a 

 diameter equal to one-si.xth the depth of the thread. The 

 catting edges are produced by a species of flute illu-strated 

 by the sectional view. It will be noticed that the cutting 

 edges aaa are evolved from a shorter radius than b b b. The 

 smooth upper portion has a diameter a trifle less than 

 that of the bottom of the thread, thereby enabling the tap, 

 when used in a plate of metal, to fall through on the lower 

 side, and so saving the trouble of screwing it back. The 

 head or shank is generally square. When the thread of 

 the tap is of uniform diameter throughout it is known as a 

 "plug" tap. 



Fig. 27 



Fig. 28. 



Fig. 29. 



Ex. LIV.— Fig. 27 illustrates 'a " taper " tap, which is 

 first made as a plug tap, the lower portion or point of 

 which is tapered down as shown at a, the amount of metal 

 removed being indicated by the dark threads b. The object 

 is that the point of the tap being of the same size as the 

 hole it is to thread, may immediately and readily effect an 

 entrance and at the same time cause a gradual removil of 

 the metal, the/arming of the threads being entrusted to 

 the upper portion of the tap. The diameter, at least near 

 the entrance, being now of full dimensions, the plug tap 

 can be introduced and the thread made parallel throughout. 



Ex. LV. — Fig. 28 illustrates a form of taper tap, not 

 to be recommended, as the threads formed at the entrance 

 by the point of the tap are only slight grooves, cut by 

 the extreme edges of the thread. The amount of metal 

 removed is very small, when compared with the work 

 performed by the taper tap, illustrated in Fig. 27. It is 

 further noticeable that the edges of the threads near the 



point, having the bulk of the work to get through, soon 

 break away, until they approach the appearance of the 

 better form of tap. 



TAP WRKNCU. 



Ex. LVI. — The tap-wrench is illustrated in Fi". 29. 

 It is a flat piece of case-hardened iron with round handles 

 and provided with a number of square holes of various 

 sizes, into which the heads of the taps are placed, when 

 the process of tupping is to bo proceeded with. The use 

 of this tool is too obvious to call for further remark. 



THE PUILOSOPHY OF CLOTHING. 



By W. Mattied Williams. 



VIII.— THE TRANSMISSION OF UEAT TIIROUGII 

 CLOTHING. 



THE fact that so small a quantity of fibrous material 

 mixed with the air in the globe of the pas.sage 

 thermometer should bring down its conducting power so 

 remarkably (see experiments 1, 2, 3, 4, 5, G, 7, 8, 9, and 

 10, page ,322) — ^\ of the volume of raw silk increasing the 

 time of cooling from 576 to 1,284 seconds — was not to be 

 passed over as a matter of course, simply because it was a 

 fact, by such a man as Rumford. He saw at once that it 

 indicated something that yet remained unexplained, and 

 therefore that further research was demanded ; a research 

 which led him to most important discoveries in the laws of 

 the propagation of heat. 



Referring to the articles on Heat in the Cyclopredia of 

 Chambers and Rees, published 178'J (iibout simultaneously 

 with these experiments), also to the third edition of " The 

 Encyclopedia Britannica," 1797, and to that of Croker, 

 Williams, and Clark, 1764 (an excellent work, supplying the 

 others with a multitude of verbatim paragraphs), I find that 

 the propagation or communication of heat was then sadly 

 neglected, although the nature and origin of heat were 

 keenly discussed. The difference between the conduction 

 and conversion of heat, upon which so much in the ecoi/omy 

 of nature depends, was not at all understood. Therefore, 

 Rumford had to work it out for himself. I am treating 

 this part of the subject rather fully, as it constitutes the 

 fundamental basis of the Philosophy of Clothing, and it is 

 very interesting to follow the route by which Rumford 

 made his important discoveries. 



They present an interesting instance of how a logical 

 effort to apply pure science to practical business may react 

 in such a manner, that practical business shall become a 

 beneficent contributor to pure science. The boring of 

 brass cannon suggested Rumford's celebrated demonstration 

 of the principle that " heat is motion," and in like manner 

 the selection of the best material for soldiers' coats and 

 trousers led him to discover the convection of heat. 



Assuming, in accordance with the science of the period, 

 that the heat which passed from the bulb of his thermo- 

 meter through the matter surrounding it was transmitted 

 by conduction, the problem suggested by the above stated 

 facts was, as he says, " How does air conduct heat?" and 

 " How can air be prevented from conducting heat 1 " He 

 says : " If air conducted heat, as it is probable that the 

 metals and water and all other solid bodies and inelastic 

 fluids conduct it, tliat is to say, if its particles remaining 

 in their places, the heat passed from one particle to 

 another, through the whole mass — as there is no reason to 

 suppose that the propagation of heat is necessarily in right 

 lines — I cannot conceive how the interposition of so small 

 a quantity of any solid as 1-55 part of the volume of the 



