1867.] 



On a Transit-Instrument and a Zenith Sector. 



385 



present of peculiar interest ; and (3) the middle and southern area, found 

 in France, Spain, and Sardinia, almost wholly Lower and Mid-Silurian. 



Under this head of geographical distribution we have to deal with some 

 curious phenomena — such as concern birthplace or first appearance, 

 generic and specific, the duration of life, tolerance of conditions, mineral 

 habitats. Migration possesses great interest, with its marks, causes, and 

 modes, with its power, direction, and rate of progress, &c. 



The transport or removal of dead organic matter from place to place, 

 the remaniemenV^ of French geologists, is an important agency under 

 several aspects, especially in the formation of extensive sheets of rock. 



It now has become proper to bring to a close these few observations, or 

 rather this enumeration of heads of Natural-History subjects, by express 

 ing a confident hope that this compilation will find many and well quahfied 

 interpreters, and will be useful to geologists in general. 



Vebruary 28, 1867. 

 Lieut.-General SABINE, President, in the Chair. 

 The following communications were read : — 



I. " On a Transit -Instrument and a Zenith Sector, to be used on 

 the Great Trigonometrical Survey of India for the determination, 

 respectively, of Longitude and Latitude.''^ By Lieut. -Colonel A. 

 Strange, F.R.S. Received February 16, 1867. 



In 1862 the Secretary of State for India in Council sanctioned the pro- 

 vision of an extensive equipment of geodesical and astronomical instruments 

 of the first order for the use of the Great Trigonometrical Survey of India ; 

 and he did me the honour to entrust to me the task of designing and super- 

 intending their construction. After several modifications, the following hst 

 was adopted : — 



One Great Theodolite, with a 3-feet Horizontal Circle. By Messrs. 

 Troughton and Simms. 



Two Zenith Sectors. By Messrs. Troughton and Simms. 



Two 5-feet Transit-Instruments. By Messrs. T. Cooke and Sons, 

 York. 



Two Smaller Transit-Instruments (German form). By Messrs. 

 T. Cooke and Sons, York. 



Two 1 2-iNCH Vertical Circles {German form). By Messrs. Repsold, 

 Hamburg. 



Two Galvanic Chronographs for registering Transit-Observations. 

 By MM. Secretan and Hardy, Paris. 



Three Astronomical Clocks. By Mr. Charles Frodsham. 



The whole of these are nearly ready, and I take the opportunity of now 

 submitting two of them (a 5-feet transit-instrument by Messrs. Cooke, and 



