230 THE GEOLOGIST. 



to form one of the levers which transmits the movements of the vacuum 

 chamber to the hand. For this important improvement a prize -medal was 

 awarded to Spencer, Browning, and Co., in 1862. 



Mr. Browning's aneroids possess the following advantages : — 

 1st. They are most carefully corrected for temperature, from about 30° to 

 100° Fahrenheit, by compound bars of metal, on the principle of the 

 chronometer balance-wheel. 



2nd. They are divided by actual comparison with a Kew verified gauge, 

 every inch varying in length : other makers mark an equal scale on the 

 dial, and endeavour to regulate the works so that the movement shall 

 correspond. Any scientific person will soon see that this is a mechanical 

 impossibility. 



3rd. They have vacuum boxes made of fine hard-tempered gold, which 

 impart the property to them of returning closely to their zero after ex- 

 periencing a change of pressure of 16 inches. 



4th. They have the centre pivots jewelled, to diminish friction as far as 

 possible : greater sensitiveness is thus obtained, and from the more accurate 

 fitting of the centre staff, the instrument is not so liable to change its zero 

 in travelling. 



A card, with a table of the index errors of the instrument, is given with 

 each aneroid ; or the instrument will be sent to Kew for verification upon 

 payment of 5s., if a fortnight's time can be given. 



When an aneroid has changed its zero, it has been customary to correct 

 it by turning a screw at the back of the instrument, which acts through the 

 medium of the mainspring on the vacuum chamber. 



This, however, is attended with two rather serious objections : — 1st, it 

 alters the tension of both the mainspring and the vacuum chamber, which 

 do not settle down for some time ; and, 2nd, it alters the range of the whole 

 instrument. 



These objections can now be obviated by a beautiful but simple contri- 

 vance, suggested to Mr. Browning by Francis G-alton, Esq., F.R.S. This 

 consists in making the dial turn round on the barometer case. By this 

 arrangement the instrument is readily corrected by turning the dial until 

 the required division comes under the pointer. 



These aneroids should be held in a horizontal position while being read, 

 and not tapped previous to taking an indication. 



Teetiaey Mammalia and Shells. — The Tertiary beds of Madrid 

 contain, according to Messrs. Sullivan and O'Eeilly, bones of Anoplothe- 

 rium JPaleotherium, Antelope, Cervus, Sus, Rhinoceros, Hippopotamus, 

 Mastodon. The Tertiary dolomitic limestone near G-uadalaxara is often 

 completely full of the shells of IAmnoea planorhis, Paludina, Helix, etc. 



Eeeata in Fossil Bieds. — The following corrections in the references 

 to the Plates require to be made :— At page 18, line 12, for "see PI. IV.," 

 read see fig. 2, PI. III.; line 13, after ("fig. 115") insert see PI. IV. 

 fig. 3 ; at page 23, second line from bottom, for "PI. V.," read PI. XII. 

 It will be desirable, throughout the entire series of papers, to refer to the 

 figures in the Plate by the notations given in the Explanation of the Plates 

 at page 233, rather than by those given in the articles, as some errors have 

 occurred. — S. J. M. 



Eeeata.— Page 87, last paragraph, for " R. TJngeriana ; and Reuss's 

 R. ammonoides,'" read " R. TJngeriana, and Reuss's R. ammonoides it 

 not being intended to liken the last to R. Ahneriana next mentioned. 



