661 SEC. 16. OEOGKAPHY. 



and tripods, and the microscopes placed to observe the lines of 

 division at the extremes. 



(6.) Represents in detail the construction of the supports of the bar, and 

 slow and quick movements which it is capable of making, the con- 

 struction of the latteen and platinum bars, the details of the same 

 divided into decimilimeters, and a drawing of the level of the 

 bar. 



(f.) Details of the micrometric microscopes with movables, circles, 

 ' reference glass, lenses, and tracers. 



(rf.) Represents the comparator. Experiments to verify the studies of ex- 

 pansion in oil bath. 



(e.) Same in detail as the former. 



(/".) This plate represents the implements used by the observers to con- 

 struct and compare thermometers. 



(<?.) This plate represents Borda's bar with which the Spanish one was 

 compared. 



(12.) Geodetical description of the Balearic Islands, by Don 

 Carlos Ibaner. Madrid, 1871. 



The author was commissioned in 1864 to study the first of the geodesian 

 Catastralian districts, which are comprehended in the provinces of Castellon, 

 Valencia, Alicante, and Balearic Islands ; he verified it in the campaigns of 

 1865, 1866, 1867, and 1868. and made the necessary studies to describe and 

 interlace the three groups formed by the islands of Tviza and Formentera 

 with surrounding islets, with those of MallQrca, Cabrera, and Dragonera, and 

 with the island of Minorca and adjacent islets. Each of these groups with 

 its corresponding triangulations' is divided by first, second, and third class 

 nets. 



Each local triangulation Avas founded upon a base measured by the 

 Ibaiier apparatus, constructed by Messrs. Brunner. 



In the first part of this work will be found a description of the instruments 

 and accessories employed in this study, beginning with the new apparatus for 

 measuring bases. This consists principally of a plated iron bar, with four 

 thermometers of mercury and a plane table, placed upon tripods and supports, 

 microscopes, and lineation glasses, and reference to the beginning and end of 

 the daily work. This apparatus offers the greatest advantage over other 

 analogous instruments, for the rapidity and ease with which the measures are 

 taken, without losing the degree of exactitude required for a geodesical base. 

 It is to be employed to measure the three bases still wanting in the Spanish 

 geodesian net projected in the provinces of Cadiz and Lugo. 



The probable errors resulting from the measurement of the Balearic 

 Islands were 



Base of Ibiya + 0-401 mm , or +0-00000240 of the length measured. 



Base of Prat, Mallorca, + J-6Sl n!r -, or +0*000000794 of the measured 

 length. 



BaseofMahon (Minorca) + 7 7 0', or +0' 00000032 6 of the length 

 measured. 



The Southampton Institute has made several metrological studies. The 

 apparatus invented by Ibaner, which was connected with the bar constructed 

 by Borda, produced the most satisfactory results. 



The three other parts of this work refer to triaugulations of the three groups 

 of the above-mentioned islands. The plates represent 



(a.) Drawing representing the bar of the Ibaner apparatus in two projec- 

 tions, mounted for observation. 



(6.) Details relating to the supports of the bar and its construction. 



(c.) Microscopes; glasses and other details of this apparatus. 



