656 SUMMARY OF CURRENT RESEARCHES RELATING TO 



BENJAMIN MARTIN. 1771. 



Type — Alternatively Simple or Compound, uncorrected. 



This exceedingly elaborate instrument, of exquisite workmanship, 

 with every conceivable movement, is said to have been made for King 

 George III. Its authentic description is " Benjamin Martin's Large 

 Universal Microscope." The meaning of the word " universal " is that 

 it can be used for viewing opaque or transparent objects with- either a 

 single or double lens combination, that is to say, either as a simple or 

 as a compound instrument, and that it possessed, in addition, the joints 

 and accessories necessary to enable the user to direct his gaze in a hori- 

 zontal, vertical, or inclined direction at his choice, and to carry the 

 body of the instrument over the different parts of the stage by what 

 was then called the " aquatic " traversing motion. The triangular 

 upright stem has a compass joint at its base, and is fixed to an elaborate 

 foot, over which it is adapted to rotate. This foot is, in most descrip- 

 tions of the instrument, erroneously described as a tripod. The three 

 feet do not, in fact, support the instrument, but serve only to steady it, 

 the weight being carried by the knob in the middle of the foot. The 

 stage has micrometric movements in three directions ; it moves the 

 object over a wire scale in the eye-piece. This method of micrometry 

 was invented by Benjamin Martin, who also wrote a book about it. 

 The double mirror, as well as the stage, can be raised and depressed by 

 rack-and-pinion. The compound body can be removed and replaced 

 by a simple Microscope ; the stage also can be removed and replaced. 

 Provision is made for holding and illuminating living objects and large 

 opaque specimens. To accommodate the instrument to the case it has 

 been placed in the horizontal position, and its stage has been dismounted 

 and laid upon the table at the foot of the instrument. 



This Microscope is fully described in the Transactions of the R.M.S. 

 of 1862, p. 31. 



GREGORY AND WRIGHT. 1785. 

 Type — Alternatively Simple or Compound, uncorrected. 



The makers of this instrument were successors to Benjamin Martin. 

 It will be noticed that they follow his lead by making the stem in- 

 clinable by a joint at its base, where it is fixed to a folding tripod foot. 

 The body rs attached to a movable arm, which, in turn, is carried by the 

 stem. This arm can be swung about the axis of the stem, and moved to 

 and fro in its socket, these movements facilitating the exploration of a 

 large specimen. In consequence of this adaptation such Microscopes 

 were, in the latter half of the eighteenth century, called "aquatic." 

 Focusing is effected by rack-and-pinion, which move the stem and body, 

 whilst the stage is fixed. This Microscope has a rotating multiple lens- 

 carrier nose-piece, invented by Pere Cherubini d'Orleans. 



Described and figured in Journ. Pt.M.S., 1908, p. 154. 



