598 



NA TURE 



[October 17, 1901 



torsional deformation is not sufficiently accurate to justify 

 elaborate precautions against bending moments, although 

 it is not difficult to devise quite simple apparatus for 

 making these angular measurements. These simpler 

 means are somewhat overlooked by Mr. Popplevvell, but 

 an excellent account is given of the more elaborate and 

 accurate instrument designed by Mr. Coker. 



We are glad to find that our author, while describing 

 several of the standard forms of apparatus for taking 

 autographic records, is alive to the fact that these records 

 are of secondary importance so far as the determination 

 of the properties of the material is concerned, although 

 undoubtedly of great use in exhibiting the nature of these 

 properties. In educational testing especially, as indeed 

 in all laboratory work, there is a danger of fostering too 

 great reliance on autographic records, and the supreme 

 value of first-hand observations cannot be too strongly 

 msisted on. 



It must suffice here to mention that the sections of the 

 book which deal with the tests of ropes, chains, struts and 

 so on are sufficient for their purpose, that there is a 

 useful account of cement testing, although perhaps 

 enough weight is not allowed to the personal factor in 

 mixing, and that tests of the other materials of building 

 construction are also briefly dealt with. Some account 

 is also given of the effect of varying conditions, such as 

 temperature, annealing, and bending, on the properties of 

 metals. The effect of repeated stress and of reversed 

 stress is dealt with in Chapter xi., and it would add con- 

 siderably to the practical value of this chapter if a de- 

 scription of some of the standard pieces of apparatus 

 used in making these tests were included. The account 

 of timber testing is somewhat brief, but the general course 

 of such tests IS described and some standard determina- 

 tions are quoted. 



In his final chapter Mr. Popplewell has collected and 

 tabulated a large number of determinations of what he calls 

 the strength properties of the various materials considered, 

 and this chapter, which seems both comprehensive and 

 up to date, will undoubtedly be much used for reference 

 by all who have occasion to consider these properties. 

 He also adds a bibliography of books and memoirs. 



We find no reference to the microscopic investigation 

 of the structure of metals, a subject which has so much 

 advanced of late years. The subject, indeed, demands 

 a volume to itself, and at present perhaps is more in the 

 province of the metallurgist than in that of the engineer, 

 but its application to the investigation of flaws in struc- 

 tural parts has already given it a practical bearing which 

 ought not to be overlooked. 



Throughout the whole volume the need of occasional 

 calibration of any testing machine in ordmary use is not 

 indicated, nor is any description of the methods usually 

 adopted in carrying out such a calibration given. This 

 is a matter of such importance from a practical point of 

 view that we must attribute the omission to inadvertence, 

 and it will no doubt be rectified in another edition. On 

 the whole, notwithstanding the few omissions and defects 

 to which we have thought it necessary to call attention, 

 we heartily commend the book to all who have to do 

 either with the commercial testing of materials or with 

 the management of the testing departments of engineering 

 laboratories. 



NO. 1668, VOL. 64] 



A NEW SURVEYING INSTRUMENT. 



Der Hammer-Fennel' sche Tachymeter- Theodolit unci die 

 Tachymelcr-kippregel zur unmittelbaren Lattenablesung 

 vcn Horizonlaldistanz tend Hohenuntcrschied. Von 

 Dr. E. Hammer, Professor an der K. Technischen 

 Hochschule in Stuttgart. Mit i6 Figuren im Text 

 und 2 Lithographierten Tafeln. Pp. 52. (Stuttgart : 

 Konrad Wittwer, igoi.) 

 ■pROF. HAMMER has long occupied himself with 

 -L the problem of constructing an instrument which 

 should give the surveyor the necessary data for plotting 

 his work with the least possible difficulty. Indeed, his 

 numerous references to his previous work, and to the 

 criticisms he has from time to time offered on the work 

 of others, make his introduction not a little difficult to 

 read. But, since the history of his work connected with 

 tacheometers is set out with true German completeness, 

 it may be valuable to anyone who is working on similar 

 lines. In 1893 the author began to solve the following 

 problem ; to devise a tacheometer-theodolite, by which at 

 one operation and without reading an altitude circle the 

 observer could determine both the horizontal distance 

 and the diffierence of altitude of a selected spot from the 

 instrument. This problem the author now claims to 

 have satisfactorily solved, and the instrument is on the 

 market ; but notwithstanding this long preparation we 

 gather that several small improvements touching the 

 arrangement of the microscopes and the general mount- 

 ing of the instrument are still contemplated. 



The optical part of the instrument consists of a so- 

 called Porro object-glass, in which two lenses are kept at 

 a constant distance from each other. The principal 

 object-glass has a focal length of 350 mm., and the 

 second lens, placed at a distance of 340 mm., 220 mm., 

 giving to the entire system a focal length of 335 mm. 

 The focussing is effected by moving the object-glass, and 

 the eyepiece views a diagram of peculiar construction on 

 which the effectiveness of the instrument depends. No 

 compass or altitude circle is furnished with the tacheo 

 meter, but these can be added if it is desired to use the 

 instrument as a transit theodolite or for other purposes. 

 Instead of an altitude circle, a prism is placed at the side 

 of the telescope above the axis, in connection with which 

 is a carefully constructed diagram, arranged to a scale, 

 by which can be shown the amount of tilting given to 

 the telescope. A second prism placed behind the ocular 

 throws an image of the diagram into the field of view, 

 and as the telescope is moved up or down the diagram is 

 moved to the right or left of the field, thus causing the 

 lines of the diagram indicating the amount of inclination 

 to cut the vertical wire in the eyepiece at a different 

 place. The diagram and mechanical adjustments are so 

 arranged that by multiplying the observed displacement 

 of the line from the zero by 20, the difference of altitude 

 in metres will result, while another displacement multi- 

 plied by 100 gives the distance. Very great care seems 

 to have been bestowed on the construction of the field 

 diagram on which the accuracy of the instrument must 

 much depend. The correctness of the coefficient could 

 no doubt be effectually checked by the measurement of 

 known distances and of differences of altitude. Some 

 little inconvenience, it would seem, must arise from the 



