April 17, 1SS5.] 



♦ KNOWLEDGE 



321 



it may be smooth for either one of two reasons — no 

 waves of any description may agitate it at all, or 

 the crest of one wave may tit into the hollow of 

 another, and so reduce that part of the surface to a 

 dead level. Now, let us suppose two sets of waves set up 

 in an elastic system from two separate points, and let these 

 points be so situated that the vibrations (light) from them 

 reach a third point either together or at times dill'ering 

 by exactly one wave-length, two wave-lengths, tire. Then 

 two wave-crests must simultaneously reach that point, with 

 the result of doufiliiu/ the light there. Suppose, though, 

 that the waves from our two points reach the third at 

 times differing by half a wave-length, a wave-length and a 

 half, &c., then it will be seen that the crest of one wave 

 must fit into the hollow of the other, produce a dead level, 

 and consequent darkness. It is from one wave thus inter- 

 fering with another that the phenomenon has derived the 

 name of Interference. A very little thought will suffice to 

 show how this happens in the case of waves from the two 

 mirrors ; and this idea once grasped, it will not be difficult 

 to Bee that the sharp edges of the openings, or bodies 

 casting the shadows in our first experiments, by placing 

 obstacles in the way of the rectilinearly propagated light 

 which strikes them, set up fresh systems of waves ; those 

 &om each edge interfering with each other, and alternately 

 doabling the amount of light and annihilating it. 



THE PHILOSOPHY OF CLOTHING. 

 By W. Mattieu Williams. ' ' 

 vi.— the protecting power of different 



MATERIALS. 



THE philosophy of the problem enunciated at the end 

 of my last was for the first time systematically 

 studied by Benjamin Thompson, afterwards Count of 

 Rumford. In my previous papers on " The Chemistry of 

 Cookery," I introduced this remarkable man to my readers 

 as a philosophical cook. I have now to describe some of 

 his exploits as a tailor. 



Between 1777 and 1784, he served the British Govern- 

 ment both in naval and military capacities, having 

 previously distinguished himself rather suddenly as a 

 diplomatist. He rapidly rose to the rank of colonel, but 

 could get no fighting to do, although he went to Jamaica, 

 and also offered his services to Turkey for the purpose. 

 The world had suddenly become peaceful for a short time. 



He therefore very cleverly managed to introduce himself 

 to the Elector of Bavaria, obtained a formal invitation to 

 enter his service, and returned to London to ask permission 

 from the King to do so. 



This was given, and with it the honour of knighthood. 

 Sir Benjamin then migrated to Munich, set to work at 

 once in first studying the social and military condition of 

 Bavaria, and then devising the reforms that were necessary. 



I must not turn aside to enumerate these, however 

 interesting, having at present only to do with one of them 

 — viz., the clothing of the Bavarian army. In reference to 

 this, he says: — "Having in the year lliii, with his 

 Majesty's gracious permission, engaged myself in the service 

 of the Elector Palatine Reigning iJuke of Bavaria, I have 

 since been employed by hLs Electoral Highness in various 

 public services, and particularly in arrangiug his military 

 affairs, and introducing a new system of order, discipline, 

 and economy in the troops." I may add that, on carefully 

 studying his own account of this " new system," I have 

 become convinced that the present military eminence of the 



German l'2mpire is due to the fact that the whole of Ger- 

 many subseiiuently carried out Thompson's original system 

 of order, discipline, and economy in all its details, even to 

 those of clothing material, as will be presently seen. In 

 this respect, Germany owes as much to Thompson as to 

 Bismarck and Moltke. 



His tailoring achievements were jirimarily connected 

 with his scheme of military education. He tells us that in 

 all his operations he endeavoured " to unite the interest of 

 the soldier with the interest of civil society, and render 

 the military service, even in time of peace, subservient to 

 the /nib/ic good ; " and " to establish a respectable standing 

 military force, which should do the least possible harm to 

 the population, morals, manufacture, and agriculture of 

 the country, it was necessary to make soldiers citizens and 

 citizens soldiers." 



Industrial training supplementing the primary instruc- 

 tion in his military schools was an important element of 

 this business, one department of industry being the spin- 

 ning and weaving of the materials, and the making-up of 

 the garments of the soldiers by the soldiers themselves. 



What material t was the first question. This scientific 

 and jiractical reformer had no respect for established 

 usages, however ancient, unless he could discover good 

 reasons for their existence. His question was not what the 

 soldiers had worn, but what they should wear, what would 

 clothe them the most comfortably and decently at the 

 smallest cost. 



The first use of clothing being to keep the wearer warm 

 his first inquiry was directed to find the best material for 

 this purpose. He saw at once that clothing did this by 

 resisting the passage outwards of the animal heat, i.e., by 

 virtue of its resistance or low conductivity, or " non-con- 

 ducting power," as he called it. 



Ordinary tailors would have tried experiments on human 

 beings by supplying ditTerent kinds of clothes, and con- 

 sulting the opinions of wearers concerning their relative 

 merits. But Thompson was too well acquainted with the 

 disturbing influence of prejudice to do this, and therefore 

 constructed a model soldier that would tell the truth, the 

 whole truth, Rnd nothing but the truth. 



This model wearer of clothing was a thermometer, the 

 bulb of which represented the body of the soldier. By 

 simply clothing it with determinate quantity of various 

 material, raising it to a given temperature, and then sur- 

 rounding it with definite cooling agencies, he was able to 

 measure the relative powers of the different materials in 

 resisting the passage of heat. 



He used for this purpose a mercurial thermometer, 

 whose bulb was about 55-lOOth of an inch in diameter, and 

 its tube about ten inches long. This was suspended in the 

 axis of a cylindrical glass tube about three-quarters of an 

 inch in diameter, ending with a globe I C-lOth inch in 

 diameter, in such a manner that the centre of the thermo- 

 meter bulb occupied the centre of the globe, thus leaving 

 a surrounding space to be occupied by the material to be 

 examined. 'The thermometer tube was graduated with 800 

 divisions between the freezing and boUingpoints of water 

 — i.e., a Reaumur scale divided to tenths of degrees. The 

 thermometer was held in its place by a long cork stopper. 



He named this a "passage thermometer," and constructed 

 it with many modifications to suit various experiments, but 

 the principle was the same in all. I should add that he 

 communicated several papers to our Royal Society describ- 

 ing many other experiments with such thermometers, their 

 object being to determine the conducting power of mercury, 

 water, various vapours, and vacuum, besides those on 

 clothing materials. 



He describes his method of clothing the bulb as follows : 



