MICROSCOPE. 



217 





Mi- Another method of making glass globule*, wasde- 



cr<Mcop. crjbed by Mr. Butterficld in the Phil. Trans, for 



^ ~<~"' He usetl the flame of spirit of wine, well rectified, and 



'"*f r " burned in lamp ; but instead of cotton he employed 



thod of"" * ma " s "' ver wire, doubled up and down like a skain of 



nuking thread, which being wet with the spirit of wine, and 



(lobule*, made to burn in the lamp, gives a very ardent flame. 



Having pounded some glass, and washed it very clean, 



lake some of it up on the point of a silver needle filed 



very small, and wetted. It must then be held in the flame 



til! it be quite round, and no longer ; and if the side of 



the glass next the needle is not melted, it may be put 



off, and taken up with the wetted needle on the round 



side, presenting the rough side to the flame till it be 



everywhere very round and smooth. When wiped 



with a piece of soft leather, they are ready for being 



placed between two plates of metal for use. 



Graj'f mi- The ingenious Mr. Stephen (Jray proposed to con- 

 crotcopc* struct single microscopes with drops of water, in the 

 with drop* following manner : " I take a thin piece of brass," 



'PL' MJS ' -' " into the fam AH> Fip ' '' ""'""g 



' * rna " no ' e ** A, which serves for an aperture; then 

 ::;* it by the other end B, I pour a lew drop* of 

 water on the table, taking up a small globule thereof 

 with a pin, which I lay on the hole A ; then reu 

 the pin, the water will remain on the aperture, in form 

 l.emisphere, or a plano-convex lens. But if I have 

 > make a double convex of water, I thrust the 

 pin, which must be IMS than tin- ho!.-. through the 

 Hole, till the water be entered tin-rein ; then, by draw- 

 in the pin perpendicularly to the plane of the aper- 

 ture, the water remains there in form of an aqueous 

 \e convex lens. Then, whatever I have a mind 

 w I take upon a pin, or a piece of glass, accord- 

 ing to the nature of the object ; and taking up this na- 

 tural microscope by the en 1 B 

 and fro, till it be in its : which means I can 



see i :le le-si distuutly than by glass micros- 



copes, especially by candle, which I find much better 

 than 



" But I observed, that those irregular particle* which 

 are inherent in the globules of glass, were een dis- 

 tinctly, and prodigiously magnified, as was easy to ima- 

 r nearness to the eye, and"^ because 

 not hinder the globules, cither by day or can- 

 dle ti^'ht, from appearing throughout transparent, be- 

 ing to minute as not to be discernible, except held 

 close to the eye, as in time of observation, and not 

 then neither, if too near the light, but at a competent 

 distance, they appeared as above. I knew not well 

 bow at that time to account for this strange phenome- 

 non, that an object should be placed so far within the 

 focus of a iplu riclc, a* to be within the glass, and yet 

 teen distinctly to the eye so near it ; but since, by mat- 

 ter of fact. I found it was so, I made this intt . 

 and concluded, that if I conveyed a small globule of 

 water to my eye, and that there were any opaceou*, or 

 lew transparent particle* than the water then 

 might see them distinctly. 



" Having by me a small bottle of water, which I knew 

 to have in it tome of those minute insects which Mr. 

 Leewenhoek discovered by the help of excellent mi- 

 croscopes ; having ^een them with the common glas* 

 microscopes, and with the first aqueous, as above men- 

 tioned, I poured a few drops of this water on the table, 

 and taking a small portion of it on a pin, I laid it on 

 the end of a rmall piece of brass-wire. I continued to 

 lay on two or three portions of water, till there was 

 fbrmed somewhat more than hemisphericle of water; 



VOL. T. I-AHT I. 



then keeping the wire erect, I applied it to my eye, Single Mi- 

 and standing at a proper distance from the light, I saw " 

 them, and some other irregular particles, most enor- > "~V < " * 

 mously magnified ; for whereas they are scarcely dis- 

 cernible by the glass microscopes, or the first aqueous 

 one, within the globule they appeared not much diffe- 

 rent both in their form, nor less in magnitude than or- 

 dinary peas. They cannot well be seen by day-light, 

 except the room be darkened, after the manner of the 

 famous dioptrical experiment, but most distinctly by 

 candle-light ; they may be very well seen by the full 

 moon-light. The pin sometimes takes up the water 

 round enough to shew its objects distinct." This mi- 

 croscope is shewn fitted up in Fig. 3. Fig. 3. 



In order to explain the magnifying effect of the 

 globe of water upon the animalcules, or other objects 

 placed in the inside of it, he supposes " the circle in 

 Fig. 2, to represent a sphere of water ; A an object 1~>K- * 

 placed in its focus, sending forth a cone of rays, two 

 of which are- AH, AB, which, coming into the water 

 at B and B, will be retracted from their direct course, 

 and become BD. At D they will, at their passing into 

 the air, be again refracted into DE, DE, and so run 

 parallel to each other, and to the axis of the sphere 

 A I ( '(i. Now, as the angle of reflection is equal to the 

 angle of incidence, let the rays BD, BO, be imagined to 

 come from some point of an object phcrcl within a 

 sphere of water, by btii' 1 from the iutrri.T 



nurface of tin- : c'BD is the angle of re- 



flection, to which making I'BF equal, so will F be tin- 

 place where an object, tending forth a cone of 

 two of which are 1"B, FB, which are reflected into the 

 rays BD, BD, ami then coming to the other side of 

 the sphere at D and I), they are refracted into DC, 

 as before, and consequently be as fit for distinct. 

 vision, whether tlie object be placed at F within, or in 

 A without, the sphere of iu interior surface be con-i- 

 ns a concave reflecting speculum." /'/;;/. Ti uns. 

 221, p. 280. 



: ocope i* evidently one which operates both 

 by reflection and refraction. The anterior part is a con- 

 cave mirror, by which all objects placed between its 

 surface and it* focus are magnified ; and, a* Dr. Smith 

 ha* (hewn, it magnifies object* 'S\ times more than if 

 they were presented to it in the usual manner. See 

 -Smith's OjiticM, Vol. 1 1. p. 



Mr. Gray suggested also a single reflecting micros- Gra>'< .in- 

 cope, founded on a similar principle. Let A, Fig. 4, g' reflect- 

 represent a small flat ring of bra-u, uhosc mean dia- '"> micro- 

 meter doe* not exceed /- ths of an inch, and which is !? )pc ' 

 about y,th of an inch thick. Take a small globule of *", 

 quicksilver, and dissolve it in a few drops of an ua for- y lf . 4. 

 tit, to which add 10 part* of common water; clip the 

 end of a stick in this liquor, and rub with it the inner 

 circle of the ring A, so as to give it a mercurial tinc- 

 ture. After it is wiped dry, and laid upon the table, 

 pour a drop of quicksilver within it, which being press- 

 ed gently with the ball of the finger, will adhere to the 

 ring ; and when it in cleansed with a hare's foot, it will 

 form a convex speculum. Take up the ring and spe- 

 culum, carrying it horizontal, and lay it on the brims 

 of the hollow cylinder B, and the mercury will now 

 become a concave reflecting speculum, which may be 

 used as a reflecting microscope. Phil. Trans. } 

 No. 288, p. 539. 



Single microscope*, of a very simple kind, were con- r) r . Brw- 

 structed by Dr. Brewster, by taking up drop* of very .ter's mi- 

 pure turpentine varnish, and allowing them to fall on crowopctof 

 a plate of thin and parallel glass. In this way he nili. 

 2c 



