Class X.]

SELF-REGISTERING METEOROLOGICAL APPARATUS.

299

ptrument can be so pleasing in appearance as that which,from its construction, is well adapted to its work, andlikely to lead to good and important results.

Of thermometers we cannot speak more favourably,the greater part of them being furnished with scales ofivory, a material most unsuited to a graduation of anykind; so much so, that the mercurial tube attached to anivory scale cannot rightly be called a thermometer. Thebulbs of those exhibited are nearly all too large, a defectwhich necessarily entails a very slow change of temper-ature. In self-registering thermometers there is nothingnew, and no attempt has been made to improve the work-ing of the instrument, either by the introduction into themaximum thermometer of a piece of enamel, as a sub-stitute for the steel index, or by any other means. Veryfew of the tubes of the thermometers exhibited aresunk in the scale, so that the column of mercury may bein the same plane as the divisions, or the back part of thetube cut away to attain the same object; and, what isstill more to be regretted, very few thermometers in theEnglish portion are graduated on their stems, a methodsuperior to any for insuring delicacy of graduation andcorrect readings. These remarks do not apply to theforeign portion of the Exhibition; the exhibitors it in-cludes, however, are few in number, but the instrumentsgenerally are pretty good.

No branch of physical science has suffered more thanmeteorology by the use of bad instruments. Manyjournals, after years of patient daily labour, have neces-sarily been laid on one side as useless, owing to the im-perfections of the instruments used. To judge fromthose exhibited, it would appear that as little attention ispaid now to the construction of meteorological instru-ments in London , except by a few makers, as a few yearsago, before the commencement of the systematic re-searches in meteorology at present being carried on byvery many gentlemen throughout the country.

It is to he hoped that one of the good results of theExhibition will be the calling into existence a betterclass of instruments generally, when not only shall beimproved those necessary to physical research, but thosealso which are in general use by the public. That ther-mometer is the best whose bulb is small, whose divisionsare cut on the stem itself, or engraved on well-seasonedbox-wood or on metal. That barometer is the best whichis made of brass throughout, and the mercury of whichlias been boiled in its tube ; there should be no plunger,no need of capacity correction ; and the most simplemeans should be adopted for measuring accurately thedistances between the surface of the mercury in thecistern and that in the tube, a measurement best attainedbv means of an ivory point, terminating a brass scale.

The best exhibitor of thermometers in the Exhibitionis Fastre (France , No. 511). All the instruments exhi-bited by him are distinguished by delicacy, and are pos-sessed of the essentials of first-rate instruments. Thebest exhibitors of thermometers in the British portion ofthe Exhibition are Negretti and Zamijra (No. 160),whose instruments seem to have been made with greatcare, the divisions being good, and mostly cut on thestems of the thermometers themselves. In appearancethere is but little difference between those exhibited byNegretti and Zambra and those by Fastre. The accuracyof division was not examined in either case.*

We now proceed to speak in detail of the instrumentsexhibited.

Self-registering Meteorological Apparatus.

Dolt.ond (No. 145, p. 426, and see Illustration) hasexhibited a self-registering meteorological instrument,which he has called an Atmospheric Recorder.

This instrument registers simultaneously, for any periodof time, according to the length of the paper used, thevarying pressure of the atmosphere, the changes of teni-

* To examine a thermometer carefully, and determineits index errors at every part of the scale, is very trouble-some, and occupies a great many hours ; yet every ther-mometer used for meteorological purposes should be thusexamined.

perature and evaporation, the variations in the electricalstate of the atmosphere, the fall of rain, the amount ofwater evaporated from a surface of water, and the forceand direction of the wind.

The apparatus is composed of a frame 2 feet by 3 feet6 inches, and is firmly supported upon four pillars, thesides being strongly braced together. At the distance of10 inches from either end of the frame, a roller 1 foot iucircumference is placed. That near the south end ismoved by clock-work, whilst the other acts as a reservoirfor the paper; a third, of the same dimensions, is placednear the clock or driving roller, and so arranged as topress upon it equally throughout its length for the pur-pose of keeping the paper in contact with the driving-roller.

A strong bar is placed near the north end of the frame,upon which the fulcrums of several indicators, about afoot in length, are placed. Those for registering thevariations of the barometer, thermometer, and hygro-meter, have spring points at their ends; and those for theregistration of the electrical changes, the fall of rain,evaporation, and the force and direction of the wind, havepointed pencils. The former are connected with a fallinglever, and strike the paper once in every half hour, whilstthe latter continuously mark the paper. Near the placeof registration each element has its own scale. The in-dicators are continued somewhat beyond the fulcrums,and are thus connected with the various changes of theatmosphere to be recorded. Between each element on thepaper a set of lines is drawn, which form zeros or baselines for the estimate of each. They also give a meansof correcting any error caused by the liygrometrie orother changes of the paper; on either side of the frameis a marker, which registers the time simultaneously atevery half hour.

The barometer used is on the syphon principle, in theshorter leg of which is placed a lloat, so adjusted as toleave sufficient weight to follow the mercury. The regis-tered scale trebles the actual changes. The apparatus forthe temperature consists of ten bent mercurial thermo-meters, suspended upon a delicate balance. The hygro-meter consists of a slip of mahogany cut across the grain,which was divided as follows : being suspended from itsupper end, in a cylinder filled with water, a weight of2 lbs. was attached to its lower extremity, until it wasfound, by repeated examination, to be completely satu-rated, and no longer to increase in length. Its wholelength was then referred to mi accurate scale. The slipof mahogany was then placed beside the pipe of a stove,suspended aud weighted as before, until its shortest lengthwas obtained. The difference of the two results beingcarefully taken, the scale was formed accordingly. In itsuse it is suspended and weighted as before, in a tubeplaced outside the observatory, protected from the sunand rain, and has free power to act upon the indicator.

The electrometer is constructed as follows : a well-insulated conductor is placed upon the highest convenientplace, from which a wire is brought down to an insulatoron the top of the observatory, and from thence to astandard, passing through another insulator to a metaldisc, between which and a spring a moveable disc is at-tached to a glass or insulating arm, in connection with theregistering pencil.

The electricity, in the first instance, is collected bymeans of points. There is a wire, connected with theearth, by which means any excess of electricity is dis-charged.

The rain-guage is placed on the top of the observatory,its receiving surface being 1 foot square. The rain isconducted by a pipe into a*receiver inside the observatory,and situated under the registering apparatus. An air-doatis placed inside the receiver, and connected with a set ofinclined planes, each of which is equal to a fall of rain 1inch in depth. These inclined planes, as they pass up-wards, being in connection with the indicating pencil,register the fall of rain.

The evaporating dish is an open cube of 1 foot square,covered with a plate of glass at such an angle as to pre-vent rain falling into it, yet allowing the air to act freelyupon the surface of the water.