4 REPORT — 1844. 



deduced from the second base, the difference is only 7*2 inches. Tlie difference for 

 the third is still less, being only 4-3. The instruments used in the triangulation 

 were a three-feet theodolite, considered Troughton's Capo d'opera, and two three-feet 

 vertical and azimuth circles, which also served for the celestial observations. These 

 were divided on both sides, and had four microscopes, of which two were moveable to 

 any angle. The theodolite and azimuth circles had five microscopes. The referring 

 marks for azimuthal observations and alinements of bases were heliotropes seen 

 through aperturesof a quarter of an inch. Each angle of the primary triangles isobserved 

 twenty-four times, changing the zero four times, and reversing alternately. What- 

 ever error may remain is distributed among the system according to a theorem of 

 simple application. Azimuthal observations for determining the position of the tri- 

 angles with respect to meridian, were made at fifteen different stations with the three- 

 feet circles. By careful levelling, reversing between observations and taking both 

 extreme azimuths of circumpolar stars on the same days, an unusual harmony of the 

 results has been obtained. To obtain the amplitudes of the celestial arcs, thirty-six 

 stars were selected for the northern portion of the arc ; thirty-two for the southern, 

 in each instance half being north, the rest south of the zenith. CoUimated observa- 

 tions were always taken by reversing for each star, and besides, the error of collima- 

 tion was determined by acoUimating telescope. Forty-eight observations were taken 

 of each star, and the moveable pairs of microscopes were shifted into three different 

 positions. The result is that the arc o / « 



From Damargida to Kalianpur is (3 3 55*97 



From Kalianpur to Kaliana is 5 23 37'06 



The length of these arcs in feet 1961157;117. 



It is, however, to be regretted that tliis series of triangles, and several others 

 which are described in Colonel Everest's paper, have not been filled up by any secondary 

 triangulation, or made available to any of those social purposes for which accurate 

 district maps are so important. The fault is certainly not with the Court of Direc- 

 tors, who appear from this statement to have been actuated by the most liberal and 

 enlightened views ; but wherever it may lie, in Colonel Everest's concluding words, 

 " It is to be hoped that the powers who govern India will see the necessity of taking 

 early measures to cause all these series to be filled up with topographical details in 

 keeping as to accuracy with the material now on record. At present the principal 

 triangles are in many places mere skeletons, instruments of mighty power lying 

 useless. But it seems very clear that without accurate and specific detail, whether 

 as relates to topographical or statistical knowledge, no state can be well governed ; 

 and the maps in the possession of the governing power ought for this purpose to be 

 within certain and decided limits of error." 



An Account of the Results of the Tide Observations on the Coast of Ireland. 

 By the Astronomer Royal. 



He introduced the subject by stating, that during the Ordnance Survey it had been 

 desired to fix upon a plane of reference for elevation, and that Colonel Colby had 

 been desirous of ascertaining whether one invariable plane could be obtained from 

 the observation of tides. For the determination of this, Ireland seemed to present 

 peculiar facilities ; for, during the Ordnance Survey, it had been levelled from shore 

 to shore, not only longitudinally, but also across ; the result of which was, that round 

 the entire coast many points were marked where the levels relative to one common 

 point, the sill of one of the dock gates in Dublin, were known certainly, to within a 

 very few inches. It was therefore resolved to observe, simultaneously, and for a con- 

 siderable period, the tides round the entire coast, in order to ascertain whether, from 

 their phaenomena, such a certain and readily determined plane could be deduced. 

 In these observations, besides having all the measures of height reduced to this 

 one common standard, it was also determined that all the observers should be fur- 

 nished with chronometers set to one common time, viz. mean time at the Greenwich 

 Observatory. The first peculiarity observable in the form of the coast was, that 

 while the south-western and western coast was quite open and exposed to the Atlantic, 

 the north-eastern and eastern coasts were, on the contrary, quite embayed, and in 



