156 Literary Notices, 



scale, and as the majority of observations are necessarily made 

 under a magnification which, is only a small fraction of that supposed 

 by a map of the lunar disk nearly seventeen feet in diameter, the scale 

 selected is not without serious difficulties. It certainly gives plenty 

 of room for "inserting synonyms" and "numerical data," but 

 renders objects seen under moderate powers difficult of identification, 

 and tends to induce observers to draw them on a scale dispro- 

 portionate to the amount of detail actually seen. The " best 

 possible scale," for the purpose will be estimated differently by 

 various observers ; but all agree in appreciating Mr. Birt's work, 

 which is to supply a series of lunar map sections, carefully drawn 

 to scale, and exhibiting contour lines of the various formations. 



The nature of each object is indicated by a symbol which is 

 explained in the Report of the Moon Committee for 1865, and there 

 is no attempt at a minute exactness not possible until a much 

 larger accumulation of facts has been made. Mr. Birt rightly 

 describes his charts as " a guide to observers in obtaining data for 

 the construction of a complete map." He adds, " at present the 

 engraved portions of the map are in outline, and will doubtless 

 require considerable modification, as observers work at the subzones 

 which they may select." Mr. Birt also recommends observers to 

 tint or colour their subzones, so as to make craters and other 

 objects more conspicuous than they are in the simple red outlines 

 which he provides, and which are printed in that colour to dis- 

 tinguish them readily from any corrections or additions which 

 observers may make in black ink. It would require a series of 

 elaborate notices to do justice to the numerous suggestions and 

 important bits of information which Mr. Birt supplies concerning 

 the zones and areas comprised in his map, and we can only observe 

 that they are calculated to render most valuable aid to lunar 

 students. 



It will be very interesting to compare the physical geo- 

 graphy of the earth and moon, and to notice how the distri- 

 bution of hollows, elevations, etc., vary in the two bodies whose 

 surfaces have assumed their existing forms under such different 

 conditions as are expressed by the presence, and absence, of water 

 and air, and numerous observations will be found in Mr. Birt's 

 pamphlet, which will materially facilitate researches of this kind. 

 We would take this opportunity of urging the British Association 

 Committee to lose no time in providing Mr. Birt with a telescope 

 of suitable dimensions. The small instrument which he is at 

 present using is not half the diameter of that wdiich he ought to 

 have to justify his drawing his contour lines on so largo a scale, 

 and can supply no means of testing the observations of difficult 

 objects that may be communicated to him by other observers. 



Auvergne : Its Ther.uo-mineral Springs, Climate, and Scenery. 

 A Salutary Retreat for Invalids. By Robert Cross, M.D., Edin. 

 and Heidel, F.R.C.P., Ed., and M.R.C.S.E., Author of " Physiology 

 of Human Nature. (Hardwickc.) — Geologists have long been 

 familiar with the Auvergne as a district rcmai-kable for its illus- 

 tration of volcanic action, and for the numerous extinct craters which 



