45, COENHILL, E.G., AND 122, REGENT STREET, W., LONDON. 123 



Immediately at the side of the datum line registering pencil, is a pencil 

 actuated by the clock, which causes it to trace a short vertical line at each 

 hour, through the datum lines, the mark for noon and midnight being some- 

 what different. In this case the pencil is arrested for two minutes when in 

 marking it has reached the level of the datum line, when it is allowed to 

 complete the marking. The distinction is introduced in order to facilitate the 

 subsequent noting of the times and dates upon the record. The pencil tide 

 recorder is made to counterbalance the float. wire when the scale is not too 

 greatly reduced, in which case the weight of the float- wire is partially relieved 

 by a counterpoise weight acting on the axis of the float-wheel. The system of 

 making the recording pencil balance the float- wire is a great advantage over the 

 system generally employed, and greater accuracy of recording is secured. The 

 employment of a continuous roll of paper obviates the necessity of continually 

 applying fresh paper to the recording drum, and the tide-gauge can thus be left 

 untended, except for the purpose of winding the clock, for an indefinite period. 

 The system also of ruling the paper by fixed pencils and marking the hourly 

 times by the clock constitutes a marked improvement, no error can thus occur 

 from the wrong setting of the paper. 



Prices. The Tide-guage with three barrels and continuous paper complete, best finish 95 



Ditto with single barrel and extra finish . . . .fig. 126. 80 



Ditto ditto to be used with previously divided paper . 54 



Larger engravings of some improvements in Thomson's Tide Gauge sent 



upon application. 



170. Negretti and Zambra's Portable Set of Meteorological 

 Instruments. A small, but at the same time really useful and reliable set of 

 Standard Meteorological Instruments has long been inquired for by observers 

 on foreign stations, and others who are frequently travelling to different parts 

 of the world. To meet this demand, Messrs. Negretti and Zambra have 

 arranged sets of Meteorological Instruments to pack up into a very small space. 

 The set contains ISTegretti and Zambra's Patent Maximum and Minimum 

 Registering Thermometers, Wet and Dry Bulb Hygrometer, Aneroid Barometer 

 for Altitude measurements, Negretti and Zambra's Improved Registering 

 Maximum Thermometer with high range of scale, for Hot Springs, Solar 

 Radiation Thermometer, Terrestrial Radiation ditto, Improved Boiling Point 

 Apparatus, Rain Gauge and Graduated Measure, a Clinometer, Magnetic 

 Compass, and Tape Measure. The whole arranged in a strong case; with lock 

 and key. Price 18 18 



These sets can be varied, or other Instruments added, to meet the wishes 

 and requirements of purchasers. See also pages 106 and 107. 



Further details of the construction and use of Meteorological Instruments mil 

 be found in Negretti and Zambra's TREATISE, with very many valuable and useful 

 Tables of corrections, fyc., fyc. Seepage 133. 



