288 Notices respeclhig New Booh. 



of record by his own knowledge or recollections, but has been com- 

 piled, in part at least, from loose notes and memoranda, not always 

 full, and in some cases discrej^ant. Captain Yollond, on whom the 

 duty of drawing up the account devolved, has executed the task with 

 great ability ; and it must be confessed that his intimate acquaintance 

 with the methods followed in the survey department, and the great 

 interest he manifestly takes in the subject, tend in no small degree to 

 counteract the disadvantage under which he has been placed in con- 

 sequence of his non-participation in the actual measurement. But 

 •while we willingly concede all praise to the editor of the work, we 

 cannot forbear remarking on the circumstance, that the account 

 of so essential and important a part of a great and costly national 

 undertaking is given to the country without the name of the officer 

 who was officially charged with its superintendence. 



The portion of this volume to which the greatest interest attaches, 

 or rather would have attached, had it appeared at an earlier period, is 

 tlie description of the measuring apparatus, of which no detailed ac- 

 count had been published, and little more was generally known than 

 that it had been invented or suggested by Major-General Colby, and 

 was constructed on the principle of eliminating the effects of varia- 

 tions of temperature by compensation or self-adjustment. But in- 

 formation on this subject has now also been supplied by the publi- 

 cation of Colonel Everest's late work on the measurement of two arcs 

 of meridian in India, in which a similar apparatus used for the mea- 

 surement of the bases connected with those operations is minutely 

 described. Captain Yollond gives the following as the reasons which 

 led to the adoption of the method in question : — 



" All the methods of measuring base lines which had been in use 

 previously to the commencement of the present survey, were more 

 or less dependent for their accuracy on the knowledge of the tem- 

 perature of bars or chains when applied in measuring. But as the 

 temperature of the air is seldom equable for any considerable portion 

 of the day, and the time which substances occupy in heating or cool- 

 ing varies according to their nature, their masses, and their surfaces, 

 it did 7iot appear that a thermometer had heen or could be devised which 

 loould give the knowledge of the temperature of a bar or chain through- 

 out its whole length at the moment it was used as a measure. This led 

 to the principle of compensation ; a principle which had long been 

 in use in pendulums, and which had been applied to them in many 

 ingenious ways." — P. 7. 



We demur to the opinion stated in the sentence we have printed 

 in italics. The apparatus used by Delambre in the measurement of 

 the bases for the French arc of meridian, indicated the relative 

 lengths of a bar of copper and a bar of platina, and thence gave the 

 absolute expansion of the platina or measuring bar " throughout its 

 whole length at the moment it was used as a measure." Bessel's 

 apparatus (on the same principle, though differently constructed) 

 also showed the expansion of the measuring bar at the time it was in 

 use. In both cases the apparatus formed of itself a metallic thermo- 

 meter ; and we conceive that the expansion (for which alone a know- 



