( 151 ) 

 NOTES AND CORRESPONDENCE. 



Fi9i4U>i-s and iitdicators. — Since Mr, Tvrrell first broached tlie 

 idea ot a finder, the subject has frequently engaged my atten- 

 tion, and although my own modification of his instrument 

 enabled me with great ease to hit upon any object, however 

 minute, even when using a plain stage to which the original 

 was not adapted, I yet became early aware that a great 

 improvement would be effected if the ivory slip could be 

 altogether dispensed v/ith; as it required, when using high 

 powers, more steadiness of hand lor its accurate use than 

 many people are fortunate enough to possess, and as the read- 

 ing the figures through the microscope was not always easy. 



Dr. Wright's contrivance, which appeared in the same 

 number of the journal as my own, was very satisfactory as far 

 as the individual microscope for which it was used was con- 

 cerned ; but as no two makers form their instruments exactly 

 on the same principle, it was inapplicable to a great number 

 of moveable stages, although in the modified form suggested 

 by Dr. Wright at the end of his paper, available for plain 

 ones. It had, too, the disadvantage of being non-transferable 

 (or " selfish," as Mr. Bailey calls it), from which charge, by 

 the way, I must defend Mr, Tyrrell's and my own instru- 

 ments, inasmuch as they formed very convenient packing 

 cases for slides, and it was only necessary to wrap them in 

 paper, and enclose them in a twopenny stamped envelope to 

 insure their safe carriage to your correspondent. My own 

 was suited for the use of any microscope, and was in this 

 sense an " Universal Indicator ; " its great drawback was, as 

 I have stated, the ivory slip. I next tried the vertical and 

 horizontal scales ruled on card, but failed from my inability 

 to insure satisfactorily an uniform position for it on any and 

 every moveable stage ; in fact, the idea wanting was the 

 ingenious one of Mr. Bailey — the separate central piece for 

 continuing the vertical and horizontal lines to their intersec- 

 tioa The instrument which I now forward you (a rough and 

 home-made specimen), and of which I also enclose an out- 

 line, is used with the greatest possible ease, and appears to 

 me to possess the following advantages. Its steadiness is suffi- 

 ciently insured by a side check to the left hand, which rests 

 against the stage. The hole in the middle of the boxwood is 

 furnished with a rabbet or ledge for the reception of a disk of 

 bone, perforated accurately in the centre with a very small 

 needle, and which can be entirely and steadily removed by 

 seizing a little brass peg attached to it with the forceps. 



