APPENDIX II. 421 



great variety of substances, but I send you the result of 

 such observations as I have made, which will be sufficient 

 to enable you to judge of the accuracy of the instrument. 



Fibres of coarse wool from green baize, 52. Southdown, 

 35. Anglo-merino from a flock of Mr. Henty Tarring, 27. 

 A lock taken from a Paular ewe by Mr. Sheppard, 25 

 (varying from 24 to 30). Another specimen from the 

 same flock brought by another gentleman as a test of the 

 instrument, 25. Cotton, mixed but about, 19. Vigonia 

 from the Rev. P. Wood, very distinct 14J. Beaver from a 

 hat, 11. Blood diluted with saliva and rubbed on glass, 

 beautifully distinct 5. Milk diluted with water, very in- 

 distinct 3. I have sometimes thought of employing the 

 instrument as a nosological test of the state of the blood, 

 of pus, and of other animal fluids. 



It is of little consequence to the farmer to know the 

 actual dimensions indicated by these numbers, nor can I at 

 present ascertain them with perfect accuracy. They ex- 

 press, however, very nearly the diameters of the fibres in 

 the 45,000th of an inch. Thus Mr. Henty's wool, standing 

 at No. 27, must measure about ? ^oir or Wsr f an i ncn * n 

 diameter, and the globules of the blood reduced to spheres 

 about -^oW' Probably these results are a little too small, 

 and especially the latter, but by a comparison of a few 

 measurements, made by means of other micrometers with 

 these numbers, it would be easy to form a correct table of 

 their true value, and it may safely be asserted that this in- 

 strument will enable us in some cases to be secure of 

 avoiding any error amounting to the hundred-thousandth 

 of an inch, and almost in all of being far within one ten- 

 thousandth of the truth, without the use of any microscope, 

 simple or compound. 



En order to render the instrument still more portable we 

 may employ a piece of tape as a measure, fixing to one end 

 of it a double piece of card with an aperture, and with some 

 pins projecting from its edge for holding the wool either 



