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Mr. E.T. Lewis exhibited and described a new Gange which had recently 

 been invented for the purpose of readily ascertaining the thickness of wires 

 or plates, and which was capable of indicating the results with accuracy to 

 the yo^o of an inch. He thought perhaps some apology might be needed 

 for troubling them with a matter which was not strictly of microscopical 

 interest, and had not the excuse of being made of either brass or glass ; but 

 although, so far as he was aware, its inventor had not intended to apply it 

 to any microscopical purpose, it had been found of use in the measurement 

 of glass slides, cells, and covers, and as such he had been asked to bring 

 it to the meeting. It was really made for the use of electricians and 

 engineers, to replace, with considerable advantage, the old form of wire 

 gauge, which merely consisted of a steel plate having a series of slots cut 

 in the edges, each of which was numbered according to an agreed scale. 

 The article to be gauged was tried in these, and the number of the one into 

 which it most nearly fitted was said to be its " gauge." Eecently, the 

 question of gauges had been considered by Chambers of Commerce, and as 

 it appeared that those in common use were often at variance, a new 

 " Standard Wire Gauge " had been agreed upon, and with the sanction and 

 authority of the Board of Trade now superseded the old Birmingham Wire 

 Gauge. The differences between the two were not sufficient to alter the 

 number of the gauge, though when subjected to accurate measurement it 

 would be found that these differences ranged from 1 to 5 thousandths of 

 an inch. For purposes of scientific or international measurement it was 

 frequently desirable to express thickness in fractions or decimals of the 

 inch or millimetre, and the ordinary form of gauge was quite useless for 

 this purpose ; there was too much difference between the sizes, and any 

 attempt to measure by means of a ruled standard micrometer would render 

 only imperfect results, even where hundredths of an inch were attempted. 

 The new gauge before them (known as Trotter's Patent) was, however, 

 capable of showing at a glance, and by one operation, not only the Standard 

 Gauge, but the proportional part of an inch to 3 places of decimals, and that 

 of the millimetre to two places of decimals. The instrument was of 

 polished steel, in size 2|in. long and ^in. wide, and made in two pieces 

 which were accurately fitted to slide one in the other by means of a dove- 

 tailed groove, the edges of the outer section being milled for convenience 

 of holding whilst the inner slide was being moved. On the lower edge of 

 each section was a scale divided and marked by figures from 6 to 40. The 

 upper edge of the outer section was divided for the space of 1 inch into 

 lOths and 50ths, and the adjoining space for the length of 1 centimetre was 

 divided into millimetres and halves. The modus operandi was explained 

 by means of a diagram, it being simply necessary to open the slide, and 

 having pressed the substance between its jaws, to read off the required 

 measurement from the scales. The Standard Gauge was ascertained by 

 finding which of the two identical numbers on the lower scales were coin- 

 cident ; in the diagram these were the 16's, so that the thickness was deter- 

 mined to be number 16 s.w.g. Turning to the upper 1 inch scale, it was seen 

 that the arrow head of the zero mark was slightly beyond the third division 



