APPENDIX. 949 



2857b. Negretti and Zambra's Standard Dry and Wet 

 Bulb Hygrometer or Fsychrometer. Negretti and Zambra. 



Two thermometers as nearly identical as possible are placed side by side, 

 one marked DRY and the other WET. The bulb of the wet thermometer is 

 covered with thin muslin, and has twisted round the neck conducting threads 

 of cotton, passing into a vessel containing water placed on one side so that the 

 water may not affect the reading of the dry bulb thermometer. The tempera- 

 ture of the air and of evaporations is given by the reading of the two thermo- 

 meters, from which can be calculated the dew point. 



3039 a. Collection of Drawings in illustration of the pro- 

 gress in the construction of instruments employed in the science of 

 geodesy, selected from various works published by the contributor. 

 Dr. Wilhelm Tinier, Professor of Practical Geometry at 

 the I. R. Polytechnic Institute at Vienna. 



Illustrations of the Improvements in the construction of Surveyors' or Engineers' 



Tables. 



1. Drawing and description of Praetorius's table (1576-1616), after Daniel 

 Schwenter (1623). 



2. Drawing and description of Marinoni's table (1676-1755). 



3. Kraft's table (1827), A., page 334. 



4. - Starke's table (1859 and 1873), A., page 336. 



Illustrations of the Improvements in the construction of the appliances of 

 sight required in the use of Surveyors' and Engineers' Tables. 



5. Drawing of a simple alidade for taking the level towards one side, A., 

 p. 340. 



6. Drawing of an alidade for taking the level on both sides, A., p. 340. 



7. Drawing of an alidade with mountain side-vanes, A., p. 340. 



8. Simple perspective index (or ruler), after Sadtler (1816), A., p. 346. 



9. Essentially improved construction of the perspective index, after Kraft 

 (1854), A., p. 352. 



10. Improved construction of the perspective index, after G. Starke (1867), 

 A. and C., p. 356. 



11. Improved construction of the perspective index, with Stampfer's sur- 

 veying screw, after G. Starke (1832-1869), E., pages 53 and 55. 



Ha. Perspective index with turning water-poise (spirit level), after G. 

 Starke (1874), M. 



Illustrations of the Improvements in the Appliances for Reading the 

 Graduated Divisions. 



12. Nunnez, Pedro-Nonius (1497-1577), proposed the employment of 

 auxiliary quadrants, variously divided (1542). 



13. Hommel, John (1518-1562), proposed using transversals for dividing a 

 circle 



14.' Vernier, Pierre (1580-1637), proposed the employment of Vernier's 

 (Nonius's) graduated scale (1631). 



14A. Ramsden introduced the micrometer (or reading microscope, 1777). 

 A., page 135, and D. 



Theodolites and Universal Instruments. 



15. Simple theodolite for land surveying, after G. Starke. A., page 259. 



16. Repeating theodolite, after G. Starke. A., page 273. 



