30 



89. Mohr's specific-gravity balance. 

 E. 43. 1889. 



This form of instrument is in many respects similar to 

 No. 88, and is furnished with tube, riders, and thermometer 

 to adapt it for use in the same way. 



The equal length of the two arms of the lever allows of its 

 serving also as an ordinary balance ; while it is fitted for use in 

 the measurement of the specific gravities of solids. 



It is made of brass, and set on a mahogany stand, having a 

 drawer to contain it when not in use. 



A cord passing over two pulleys attached to an upright, 

 allows of the balance being raised or lowered. 



H. Clinometers, fyc. Instruments used in Geological 



Surveying. 



90. Portable boring apparatus used in the geological 

 survey of Belgium. Invented by E. Van den Broeck and 

 A. Rutot ; made by J. Didion, Brussels. 



E. 55. 1889. 



A full description of the instrument, and of the work done by 

 it, is contained in the " Bulletin de la Societe' Beige de Geologic, 

 de Paleontologie et d'Hydrologie," Vol. II. 1888. A copy of an 

 extract is shown with the apparatus. 



91. Thermometers employed in determining under- 

 ground temperature by the British Association Com- 

 mittee, Secretary, Prof. J. D. Everett, F.R.S. 



(a.) Negretti's inverted maximum thermometer with 

 outer glass case to protect it from pressure. 



(&.) Phillips' maximum thermometer with sealed glass 

 case containing spirits. Designed by Sir W. Thom- 

 son ; made by Casella. 



(c.) StapfFs and Everett's slow action thermometer. 

 Made by Negretti and Zambra. 



Each of these instruments is supplied with a copper tube to 

 contain it when in use. 



E. 44, 46, and 47. 1889. 



92. Abney's combined level and clinometer. 



Lent by the Geological Laboratory, Royal College of 

 1887. Science. 



This consists of a long rectangular hollow box,, with a pin-hole 

 at one end, and an aperture at the other, so that the base of the 

 instrument may be directed accurately in a given direction 



