144 Gleanings from the International Exhibition. 



carries a diamond point, which is pressed against a thin plate of 

 glass, producing by its action a micrograph of the design over which 

 the long arm of the lever is traced below. The apparatus is a modi- 

 fication on that originally designed by Mr. Peters, and produces 

 effects which have not hitherto been obtained. As examples of its 

 power of executing fine writing, it may be stated that the entire of 

 the Lord's Prayer may be easily written in a space of the one 2500th 

 of an inch, and the entire of the first chapter of St. John, containing 

 51 verses and 4137 letters have been written in less than the one 

 thousandth of an inch, a degree of minuteness which would enable 

 the whole Bible to be written in the space of two square inches. 

 Notwithstanding their excessive minuteness, the letters are easily 

 legible under a high magnifying power, each line being perfectly 

 distinct. The instrument is equally applicable to the engraving of 

 linear designs. Amongst those that have been engraved, and which 

 are exhibited by Mr. Webb, may be mentioned a long geometrical 

 spiral in the one 2000th of an inch, and a comic illustration of a joke 

 of Captain Marryat's which can be covered by the point of a pin. 



The true value of the instrument, however, is shown in its appli- 

 cation to the purposes of microscopic science ; it is capable of pro- 

 ducing Robert's microscopic tests in bands of lines numbering 

 100,000 to the inch, and micrometers with divisions rising to the 

 one 4000th of an inch, which, when crossed, produce perfectly dis- 

 tinct and sharp angled squares, each of one-sixteenth millionth of 

 an inch in size (4000 X 4000 = 16,000,000). 



As our notice may be the means of sending many to look at 

 these astonishing results, it may save some trouble by stating, that 

 having been introduced during the last few days, the micrograph 

 will not be found in the catalogue, but its locality is readily ascer- 

 tained as it is placed against one of the pillars of the northern gal- 

 lery, on the railing overlooking the court below. 



Analysis of New Minerals in the Exhibition : Dysodile. — In 

 the Museum of Practical Geology, in Jermyn Street, will be found 

 a large mineral mass labelled somewhat in the following style : — 

 " Combustible matter from the banks of the river Mersey, north side 

 of Tasmania." Specimens of the same substance are also to be seen 

 in the Tasmanian Court of the International Exhibition, and it seems 

 certain that this " combustible matter" is nearly identical with a 

 rare mineral described as dysodile in Chapman's Mineralogy. It pre- 

 sents the appearance of a brownish-grey slate rather than that of 

 any kind of fuel ; yet it burns freely, though with a very offensive 

 smell, when held in a flame. It has been employed in the locality 

 of its occurrence instead of coal. 



Examined with a magnifying lens of low power, the combustible 

 constituent of dysodile is seen to be disseminated pretty uniformly 

 through the mineral in the form of small flattened drops of a pale 

 brownish-yellow colour, and marked with a few ridges radiating from 

 the centre of each disc. When a piece of dysodile is crushed in a 

 mortar, and the fragments warmed with strong hydrochloric acid, 

 these discs float in the liquid and may be easily separated. They 

 are nearly, if not quite insoluble in ether, alcohol and benzol, thus 



