ANEROID BAKOMETER, 



The most accurate instninient for this purpose is the ordiuary 

 mercurial barometer, arranged in as compact a form as possible, aud 

 swinging by the centre from a tripod stand, when it is known as a 

 Mountain Bakometee. Even in this form it is, however, of considerable 

 weight, of awkward form, and liable to break. 



The Hypso.metee is a simple instrument, consisting of a thennometer 

 inserted in a partly closed vessel containing a little water, which is made 

 to boil by means of a spirit lamp. Now on a mountain top, the water 

 being under less pressure, will boil at a lower temperature than at 

 the sea level. Thus Tjiidall found the boiling point of water on the top 

 of Mont Blanc to be 185" F., showing a lowering of the boiling point of 

 1° F. for every a'JOft. of ascent. • 



The Syjipiesometee, invented by Adie, of Edinburgh, measxix'es 

 pressure by means of a glass tube some 18in. long, closed at one end 

 and bent round at the other. The lower part is iilled with glycerine, 

 and by the varying pressure of the outside air on this iiuid, the air in the 

 upper part of the tube is compressed or allowed to exjiand as the case 

 may be, the amount being shown by a scale marked on the tube. 



Lastly we have the Aneeoid Baeojietee, which consists of a thin, 

 hollow corrugated metallic box, almost exhausted of air, and the hd of 

 which is prevented from sinking too far in by a strong spring which is 

 attached to it. The spring is connected with levers, which move a 

 pointer over a graduated dial. When the pressure of the air increases, 

 the hd of the exhausted box is forced further in and the pointer moves 

 in one direction, and rice I'i'rxa should the air become lighter. All 

 aneroids are graduated by comparison with a standard Mercurial 

 Barometer, and they vaiy in size from 2in. to 12in. in diameter. 



A few months ago it was proposed to attempt the construction of an 

 accurate topographical model of Leicestershire, comimenciug with the 

 Charnwood Forest district, and gradually adding square by square of the 

 region around lantil the whole county was shown in relief. The model 

 once executed several casts could be taken from it, aud it is intended to 

 colour one of these geologically, and to show river-basins, the distribu- 

 tion of plants, etc., on a second. Such models would teach many 

 important lessons, would be interesting and instructive to eveiyoue, and 

 the very task of construction could not fail to yield valuable results. 

 The best method of executing such models I hope to lay before readers of 

 this joui'nal on some future occasion. 



Having obtained a plain Ordnance map of the district we inhabit, 

 if we desire to ascertain the height of the places named thereon, we 

 must refer if possible to some standard. Now the Ordnance Survey 

 published in 1861 an "Abstract of the principal lines of Spirit Levelling in 

 England and Wales," gi"ving to a fi-action of an inch the heights of some 

 thousands of stations. Li this valuable work are given the heights of 

 many points between Rugbj' and Leicester, between Leicester and 

 Burton, and between Leicester and Nottingham, which heights are 

 indicated upon public biiildiugs, &c., by means of the well-known bench 

 mark 1^. The points thus marked would then serve as starting points or 

 for reference, but it is necessary to ascertain the height to within a foot 

 or so of a great many other places, and after a consideration of the 

 various instruments- described in the early part of this article, it was 

 determined to use a new form of aneroid, invented by Mr. Rogers Field 

 and made by Casella, and a gi'ant for the purpose was obtained from 

 the Literary and Philosophical Society of Leicester. 



Most aneroids have attached to them a scale of feet ; in some this is 

 moveable, the altitude being obtained by setting the zero of the scale at 

 the lower station to correspond with the position of the hand, and then 



