UM 



METEOROLOGY. 



[TIIEBMOMETEBS. 



tor of Rutherford's construction, pushes a registering- 

 pin before it M the mercury expands by heat ; on the 

 Fit. n. 



sir becoming cooler, the mercury contracts, leaving the 

 registering-pin at the point of maximum heat. One 

 objection to tbis instrument will always be felt i. e., 

 the pin is not unlikely to become entangled with the 

 mercury, especially if the mercury should oxidise. 



It is very desirable to incline Rutherford's maximum 

 thermometer from the horizontal position, BO that the 

 bulb shall be slightly the highest, in order that the 

 thermometer may have the assistance of gravitation in 

 pushing the pin forwards. Within the last fifteen years, 

 many of Rutherford's construction have, at the Highfield 

 House Observatory, become useless, owing to the regis- 

 tering-needle becoming entangled with the mercury. 

 Two thermometers, however, of this construction deserve 

 to be noticed the one purchased of Dollond, and the 

 other of Bennett : they have done their duty satis- 

 factorily, and are at the present time in perfect working 

 order. 



Negrettft Patent Maximum Thermometer. Too much 

 praise cannot be given to this ingenious invention, 

 which, from the circumstance of doing away with the 

 registering-needle, prevents the possibility of the instru- 

 ment getting out of order. Since the invention, half-a- 

 dozen of these thermometers have been constantly em- 

 ployed by us without any derangement. The principle 

 of the thermometer is this : A small piece of enamel is 

 pushed into the thermometer tube near the bulb, and 

 the tube is then bent so as to secure it in its place ; if 

 the thermometer act once, it will continue to act until 

 the instrument is broken. As the temperature rises, 

 the mercury will flow over this enamel ; yet, on the air 

 becoming colder, the contraction will only take place 

 below this point, the whole column of mercury in the 

 tube being left to mark the maximum heat. It is only 

 requisite to turn the thermometer in a vertical position, 

 and give it A gentle shake, when the mercury will descend, 

 and flow over the obstruction, which, in the horizontal 

 position, had prevented it from returning into the bulb 

 uf tile tlii-riiiometer. 



PMM/tt*! Co>wtrncti<m of the Maximum Thermometer. 

 This, the invention, of Professor J. Phillips, F.R.S., 

 also records without a registering-needle. A small 

 bubble of air is passed down the tube, and a portion of 

 mercury is made to remain above this bubble ; as the air 

 Increases in temperature the whole column rise* ; yet, 

 when it cools, the mercury only falls from below where 

 the bubble of air is situated. It is an instrument liable 

 topt out of order in travelling ; yet, when once pro- 

 perty fixed, does its work well In consequence of the 



bubble of air expanding with an increase of temperature, 

 a slight error will be occasioned, and the thermometer 

 will read a little too high in warm weather, and the 

 reverse in cold. 



The Minimum Thermometer, until lately, has been 

 filled with spirit instead of mercury, with a slender glass 

 pin floating in the liquid. This pin is carried down with 

 it to the lowest point ; on the temperature rising, this 

 pin is left behind, and thus marks the coldest point. 

 Like the maximum thermometer, gravitation should be 

 allowed to assist the descent of the pin, which is accom- 

 plished by slightly lowering the bulb from the horizontal 

 position. The best that we have received have been from 

 Messrs. Nogretti and Zainbra ; in these the pin is much 

 longer and more slender, and they very rarely get out of 

 order. A disadvantage will always bo fult with spirit 

 thermometers, for their action differs from those filled 

 with mercury. 



The Mercurial Minimum Thermometer. Meteorolo- 

 gists have for some time urged the opticians to invent a 

 mercurial minimum thermometer, an invention which 

 long seemed almost to be an impossibility. However, 

 such an instrument now exists thanks to Messrs. Ne- 

 gretti and Zainbra. A thermometer, with a large tube, 

 is placed in a vertical position ; in it is a slender, pointed 

 needle, which is brought down to the surface of the mer 

 cury ; quicksilver, being heavier than the needle, the 

 latter is held above it ; yet, the needle being pointed, 

 plunges a small, but sensible, distance in the mercury, 

 which it invariably does by the side of the glass of the 

 thermometer tube. This being the case, the needle will 

 descend to the lowest degree of cold ; on the thermo- 

 meter rising, the mercury presses the needle to the glass, 

 and rises up by the side of it, instead of raising the 

 needle. Four months' working of this thermometer has 

 proved it to be a valuable invention. The instrument 

 must come into general use among meteorologists. 



The Solar and Terrestrial Radiation Thermometers are 

 made entirely of glass, the scale being engraven upon the 

 bulb itself. For thermometers continually exposed to 

 damp, the swelling of the wood, and the obliteration of 

 the index thereon, have been felt a great annoyance ; 

 consequently, the substitution of glass for wood has been 

 hailed with pleasure by meteorologists, independently of 

 its great improvement in a scientific point of view. 



The white enamel placed along the back of the ther- 

 mometer tube an invention of Negretti and Zauibra's 

 is now becoming generally adopted ; the improvement is 

 at once manifest on inspecting two instruments, the one 

 with, and the other without the enamel. 



The Wet and Dry Bulb Thermometer. The dry bulb is 

 the ordinary thermometer ; and the wot bulb differs only in 

 having the bulb enclosed in a muslin bag, with a cotton- 

 wick conductor to a cup of water, so that it shall always 

 be wet from the capillary action of the cotton conveying 

 the water constantly to it. If the muslin bag were at- 

 tached to self-registering, instead of ordinary thermo- 

 meters, the greatest heat and cold of the wot bulb would 

 DO obtained an important addition to the meteorological 

 instruments, yet one almost unknown. The muslin and 

 cotton should bo changed every month. 



Bennett's Photographic Wet and Dry BiJb Thermometer 

 a an additional evidence of the close relationship between 

 icat and light. In this most ingenious contrivance, 

 'ight is incessantly writing down the heat of the air. It 

 is simply requisite to place a sheet of photographic paper 

 upon the roller once a- day, in order to record every 

 change in temperature of the wet and dry bulb for the 

 twenty-four hours. This is, indeed, a triumph of 

 science. 



EVAPORATORS. Having had constructed gauges of 

 various sizes, we are enabled to speak with confidence as 

 to their working. The water in gauges under eight 

 inches in diameter becomes too warm, owing to the small 

 quantity that can be contained in them ; consequently, 

 an excess of evaporation results. There are two gauges 

 to be recommended : the one Newman's, and the OHMT 

 Negretti's. These gauges work well. Newman's is a very 

 convenient and ornamental instrument, having a gradu- 



