Royal Astronomical Society. H3 



serviceable to the common end ; as when a drain is cut through a 

 marshy soil, and the waters of numberless useless pools are collected 

 and led into one straight channel, which carries the improver through 

 the before impracticable region, ready to apply his whole energy on 

 the space beyond. But although much of this may be said of the 

 Greenwich documents, still the original observations were so fairly 

 and fully stated, and are so completely preserved, that they now 

 iulmit of reduction with the same exactness as at the time when they 

 were made. Still it is by no means a simple task to make one's self 

 conversant, not only with the merits, but with all the peculiarities, 

 the weaknesses, and the failings of both instruments and observers 

 for a period of eighty years, as the Astronomer Royal has done. 



The contents of this precious work are comprised in a quarto 

 volume of above 700 pages, excellently printed, and divided into five 

 sections. The first is devoted to the ascertaining of the clock errors, 

 comprising the intervals of the wires, corrections for imperfect tran- 

 sits, and the position of the instrument, the effects of personal equa- 

 tion, and the rules by which the fundamental and' determining stars 

 were chosen ; the second section contains the investigation of index 

 errors and zenith points of the mural quadrants and circles ; the 

 third exhibits the computation of the geocentric places of the planets, 

 as deduced from actual observations ; the fourth shows the compu- 

 tation of the geocentric places of the planets, from the best existing 

 tables of each of the bodies ; and the fifth section gives the compa- 

 rison of the observed with the tabular places, and expressions for the 

 discordances in terms of the heliocentric errors of the earth and 

 planets. These sections are briefly yet luminously described in an 

 introduction of only thirty-four pages : but, though short, it would 

 be difficult to name another specimen of astronomical writing of 

 equal clearness and excellence. There are then twenty pages of the 

 errata detected, either in the published volumes of the Greenwich 

 Observations, or in the fundamental tables on which the planetary 

 computations are founded ; and the book concludes with nineteen 

 skeleton forms of the schemes employed in reducing the matter. 

 The whole is so lucidly and methodically arranged, that any one with 

 a very moderate amount of elementary knowledge can take up an 

 observation, and conduct the process to the end ; for he will be able 

 to check every important step in the result by a reference to the vo- 

 lume itself, to the formulae, and to the skeleton forms. 



But if I may venture to express my opinion on this point, I would 

 add, that it is very improbable that a casual examination of the steps 

 of the processes should produce any useful result beyond that of 

 gratifying a laudable curiosity, or familiarising the student with cal- 

 culations and investigations of this kind. In all cases of doubt, the 

 original documents have been consulted, and every effort which great 

 experience and singular acuteness could suggest, has been made to 

 clear up the mistakes which will always be found in large quantities 

 of observation. The mode of exhibiting the results is a great safe- 

 guard against errors of computation, and in passing through the 

 press every portion of the work has been subjected to a most scrupu- 



