154 EIGHTH REPORT — 1838. 



of dark glass, making an angle of about 40*^ with the foot of the Go- 

 niometer, an improvement which appears to have been invented inde- 

 pendently by Mr. Sang and M. Degen, enables the observer to use an 

 object seen by reflection for the lower signal. The whole packs into a 

 case, the external dimensions of which are 5'5 inches long, 4'9 inches 

 wide, and 1*7 inch thick. 



A short Accoimt of a Method by which Engravings on Wood may he 

 rendered more useftd for the Illustration and Description of Ma- 

 chinery. By C. Babbage, F.R.S. 



The principle of this method consists in making one woodcut, which 

 represents a plan or projection of any piece of machinery. Several 

 stereotype plates are then taken from this block, from each of which 

 various parts of the mechanism are cut out, leaving only such parts as 

 may be clearly understood together. 



The author illustrated this plan by impressions from several compli- 

 cated woodcuts, intended for the description of his calculating engine. 

 From one of these originals five stereotype plates had been taken and 

 properly prepared. By removing certain parts from two of these 

 plates, two different parts of the machine were shown ; and by taking 

 two other pairs of stereotype plates, each of these separate parts was 

 again shown as dissected — one plate containing nothing but the fram- 

 ing supporting that part, and the other nothing but its moving parts. 

 The author suggested the employment of this method for colouring 

 geological maps. 



On the Odontograph. By Professor Willis, F.R.S. 



Professor Willis described his instrument called the Odontograph, 

 designed for enabling Avorkmen to find at once the centres from which 

 the two portions of the tooth are to be struck, so that the teeth may 

 work truly together. The position of these centres is pointed out by 

 theorv, and this instrument may be considered as the practical means 

 of carrying out the theory *. He also described the construction and 

 use of some scales of measurement invented by Mr. Holtzapfel. 



Description of an Improved Leveling Stave for Subterranean as well 

 as Surface Leveling. By Thomas Sopwith, F.G.S. 



Of late years, the method of reading the figures of the stave itself, 

 instead of using a sliding vane, has been adopted by the most expe- 

 rienced engineers and surveyors. 



The staves now exhibited are of this construction. The figures are 

 engraved on copperplate on an enlarged scale, so as to contract in dry- 

 ing to the proper length, which is determined by a \cry accurate gauge. 



* Reports of British Association, vol. vi. p. 135. 



