242 



NA TURE 



[January i i, 1900 



he has to do with a Germm book, written in German for 

 German students and workpeople, and some allowance 

 must be made for patriotism. . What would seem a fault 

 in one longitude may be regarded as a merit in another. 

 In fact, a comparison between rival methods of construc- 

 tion and the efifort to apprehend the manner in which 

 merits, fully recognised here, are appreciated abroad, 

 constitute one of the main features of interest in this 

 book. For instance, we should gather that the gravity 

 escapement is not so highly considered in Germany as 

 among ourselves. 



The separate parts of the instrument which come 

 under detailed description in the next section are axes, 

 the telescope properly so-called with its optical arrange- 

 ment, and circles. Each of these sections will be found 

 to contain excellent matter, and though one might point 

 out small omissions, to which accident has possibly 

 directed special attention, it would be ungracious to do 

 so without admitting that the author has also collected 

 numerous facts that one has either forgotten or im- 

 perfectly apprehended. Under the heading of circles 

 will be found some very interesting remarks on the sub- 

 ject of dividing engines. Whether the introduction here 

 is legitimate we will not stop to inquire, for it might be 

 urged that a dividing engine is no^rrore an astronomical 

 instrument than a lathe or a screwdriver ; but the in- 

 formation is so pertinent, and, as we imagine, rather in- 

 accessible, that we cannot but welcome this slight 

 excursion from the observatory to the workshop. 



The second volume opens with an account of the 

 micrometer in all its various forms, with wires and with- 

 out. Under this second head the author places the 

 heliometer, and does not appear prepared to regard this 

 peculiar device as a complete instrument. But his 

 practical acquaintance with its use not only entitles him 

 to speak authoritatively, but supplies him with instances 

 and examples of the method of determining the cor- 

 rections. We doubt, however, if the popularity of this 

 form of measurement will increase in this country. The 

 fifth section is the only one to which we are inclined to 

 take any exception. In it we have to do with the modern 

 developments of photography, as applied to astronomy 

 whether in the determination of stellar positions or the 

 interpretation of spectroscopic results. Photometers, 

 spectroscopes, heliostats, and a variety of other appar- 

 atus are dovetailed together into this, section, with the 

 result that we miss the minute and varied detail that 

 lends a charm to so much of the work. Neither can we 

 altogether accept the author's excuse that a thorough 

 description would lead him too. far from his purpose, or' 

 that .able, authorities like Miiller and Scheiner have 

 recently discussed in detail the matter treated in this 

 section. To have compiled an account of the instruments 

 used for the determination of position would have been a 

 perfectly intelligible undertaking, and it is in fact what 

 Dr. Ambronn has accomplished with great skill and 

 elaboration. We think he would have been well advised, 

 considering the completeness on which he had planned 

 his work, to have limited his task to such instruments, 

 and refused to consider those that are more particularly 

 adjuncts to the physical laboratory. But it must be 

 clearly understood, that it is only in comparison with the 

 NO. 1576, VOL. 61] 



remainder of the book that we notice any falling off from 

 the high level which is elsewhere uniformly maintained. 

 Some 150-quarto pages with 134 illustrations is in itself 

 a treatise of considerable size and merit, and one which 

 we may accept with gratitude. 



Under the heading of "con)plete instruments" we 

 have descriptions of every kind of Transit Circle and 

 Equatorial that ingenuity has suggested and engineering 

 skill has constructed. Indeed, in some instances, such 

 as the particular form of Transit Circle suggested by 

 Dr. Common, the fertility of resource on the part of the 

 inventor has outrun the makers' capacity to realise. 

 Sextants and Altazimuths ; the .A.lmucantar and the 

 Chronodeik are not only illustrated by a profusion of 

 diagrams, but examples of results are added. It is 

 impossible to do justice either to the wealth of informa- 

 tion or the judicious arrangement which characterise 

 this section on meridional and extra-meridional tele- 

 scopes. For the numerous forms of equatorial receive 

 the same share of careful attention and historical 

 illustration as do the transit instruments. From Sissons 

 early experiment down to *the latest addition to the 

 Cambridge Qbservatory, one might say that no typical 

 construction has been omitted. The more one studies 

 the pages of this excellent encyclopicdia of astronomical 

 instruments, the more convinced will he be that it should 

 find a place on the shelves of every observatory, and in 

 the library of every instrument maker. 



The second work placed at the head of this article 

 must of necessity partake of something of the nature of 

 a manufacturer's catalogue, but it is so much in advance 

 of the usual compilations of that character, that a very 

 feeble notion of its aim and contents is gained by such 

 a comparison. The production betokens not only a very 

 considerable amount of enterprise on the part of those 

 who are responsible for its preparation, but it intimates 

 the extent of the demand for high-class instruments in. 

 Germany, and shows the manner in which that demand 

 is met and encouraged. In reading the book, or portions- 

 of it, we experience the same feeling as in being con- 

 ducted through a scientific exhibition by the ablest of 

 guides. A constant succession of pleasurable surprises- 

 meets one at every turn, in noting how difficulties are 

 smoothed away by ingenious appliances. Dr. Leiss, who- 

 is well known from his contributions to the Zeitschrift fiir 

 Instrtimentenkunde^ plays the part of the guide with a 

 skill which suggests that many of the instruments, with- 

 whose adjustments he is so familiar, owe their final form, 

 to his ingenious skill. There is no necessity to enumer- 

 ate the various classes of instruments that here find, 

 adequate illustration. All that is needed for the physical, , 

 laboratory on the side of its optical equipment, whether 

 for education or research, finds its place here. Spectro- 

 meters and spectroscopes, goniometers and polarising 

 apparatus in wonderful variety, microscopes with endless 

 accessories, are pictured and described. And not only 

 is the student considered, but the lecturer also, for an 

 excellent chapter on projection apparatus is added. The 

 one fact that stands out clearly from this wonderful dis- 

 play is the progress that has been made in recent years,, 

 both in the variety of apparatus and the excellence of. 

 workmanship. 



