On the Dramngs of the Patent Harmonic Piano-Forte. 47 



b.ind, when the lever QR falls, and the cup is at rest, the 

 vdlvc at S closes the tui.ie and prevents the spirits iVoai be- 

 ijrio wasted by evaporation. 



h is lastly to be remarked, that both the sensibility and 

 the ranee ot ihe instrument may be infinitely increased ; 

 for, on The one hand, by enlarging the proportion between 

 the diameters oF the wide and narrow parts of the tube, we 

 enlarge in a much higher proportion the extent of scale 

 corresponding to any given variation of velocity ; and on the 

 other hand, by deepening the cup so as to admit when it 

 is at rest a srealer htiglit of mercury above the lower end 

 of the luber we lengthen the column of spirits which the 

 uierciiry can support, and consequently enlarge the velocity, 

 which, with any given sensibility of the instrument, is re- 

 quisite to depress the spirits to the bottom of the scale. 

 Hence the tachometer is capable of being employed in very 

 delicate philosophical expcrlmcnls, more especially as a scale 

 njii^^ht be apjilicd to it, indicating equal increments of velo- 

 city. But in the present account it is merely intended to 

 state how it may be adapted to detect in machinery every 

 tieviation from the most advantageous movement. 



IX. Description of the Draiiings (f Mr. Loeschman's 

 Patent Harmonic Piano-Forte. 



[Continued from last volanie, p. OCT.] 



^OTE, — This description, in the specification which is en- 

 rolled in the Six Clerks' Office, is written upon the drawings 

 annexed to the specification of Mr. L.'s patent. As it 

 would exceed the limits of three, or indeed four of our 

 plates, to have given the figures of sufficient size to have 

 engraved the names of each part upon the drawings, we arc 

 corupelled to omit these names in the plate ; but to render 

 the whole equally explanatory, we have put the references in 

 this form. 'J'hc reader must be aware that on this account 

 it is not to be considered as an offieial copy, though it con- 

 tains the substance of the specification, indeed the same 

 words, but in a different form. 



In the profile or longitudinal section of this instrument, 

 (Plate IX, fig. 1, vol. xxxvii.) the following parts are the 

 ^aiiie as the mslroments now in use: A the finger-kcvs, 

 B the raised black keys for flats or sharps, C centre-piece 

 of the keys, and D centre-pins; K the key-frame, F the 

 bottom of the instrument, G the name-board, H the rest- 

 piu block, and li the pins fur the strings ; i the leaver at- 



tachvd 



