VIII. MACHINERY. 475 



write ; and for facilitating writing in darkness or an unsteady light. 



Elliott Brothers. 



By means of Dr. Thursfield's apparatus anyone can write with equal 

 facility in light and darkness. For those with defective or failing sight it is 

 of the utmost value at all times, as when used in ordinary daylight no writing 

 is visible, and the involuntary following of the writing by the eye is prevented. 

 In cases of incipient cataract, and other ophthalmic diseases requiring rest, or 

 after operations on the eye, it has been found a most valuable therapeutic 

 agent. To literary men, travellers by railway or steamboat, and others com- 

 pelled often to write in a bad or unsteady light, the invention will prove or 

 great service. No ink or pencil is required, but the writing is equally legible 

 and indelible. The mode of using the apparatus is very simple, and where 

 any sight remains will at once be comprehended and found easy of execution. 



2O54a. Feters's Machine for Microscopic Writing, 

 combining Ibbetson's Geometric Chuck. 



Royal Microscopical Society, London. 



With this machine any combination of bicycloid curves can be produced 

 on a scale wonderfully minute. Many beautiful and complex designs of this 

 kind have been engraved on glass with remarkable precision, in the space of 

 a circle the fiftieth of an inch in diameter. 



A disc the one-hundredth of an inch in diameter appears to the unaided 

 eye as a mere point, yet that point, not larger than the full-stop of ordinary 

 print, will contain five circles each, the three-hundredth of an inch in diameter, 

 and in a circle of that size (that is, about the size of a transverse section of a 

 hair of the human head) the Lord's Prayer is written and can be read. It 

 has also been legibly written in the three hundred and fifty-six thousandth 

 part of an inch. In this specimen the writing is so small, that, in similar 

 characters, the Bible and Testament together (said to contain 3,566,480 letters) 

 could be written twenty-two times in the space of one English square inch. 



The name and address of Mr. " Matthew Marshall, Bank of England," has 

 been written in the two-and-a-half millionth part of a square inch. 



2054b. Facsimile Drawing and Writing Apparatus. 



S. F. Pickler, London. 



2055. Apparatus for filling Manometer Tubes with 

 Mercury to any height. 



Prof. Dr. R. A. Mees, Director of the Physical Laboratory 



of the University of Groningen. 



The end of an india-rubber tube is screwed into an opening in the base of 

 the manometer. A wooden vessel filled with mercury is elevated by means 

 of a vertical iron rod to a height nearly corresponding with that desired in the 

 manometer tubes. With the aid of a piece of wood, which is plunged into 

 the wooden vessel, the exact adjustment of the mercury to the required height 

 in the manometer can be effected. 



2056. Diagrams illustrating the principles adopted in con- 

 structing Wood-planing Machines. These diagrams are used 

 in lectures on Applied Mechanics at the I. and R. High School of 

 Agriculture and Forestry, Vienna. 



Dr. William Francis Exner^ Vienna. 



In the forestry section of the above school, series of lectures on the 

 mechanical technology of wood-working are delivered annually. These are 



