C ^4^ ) 
This Tnftrument with a little variation may be made 
a Reflecting Microfcope ot Water, if inftead of the 
Ring G there be only a fmall Arm with a hole in it to 
receive a drop of Water, and the Cylindrick VefTel B 
be either taken away or fcrewed on with its bottom 
upwards, Co as to make an Objeft Plate, and this will 
be found more convenient for viewing the Textures of 
Opacous Objed:, then that defcribed in N** zrj of the 
Tranfadions, which is more fit for Fluid-iiKd Tranfpa- 
rent ones. 
I have begun fome Experiments towards a way of 
making a large Concave Speculum for Burning Glaf- 
fes, and have proceeded (6 far, as to find Materials that 
will naturally receive their true Figure, though of many 
Feet in Diameter, but have not yet overcome the dif- 
ficulties of giving them a good Polilh. 
VIL ExtraSi of two Letter the one to Dr. Wil- 
liam Gibbons^ Fellow of the College of Phyfiti- 
ans London ; the other to Mr. Nicholas Sta- 
phorft 5 Operator in Chymiflry at Apothe- 
cdLties-Hallj from Mr. Edward Coles, giif^ 
ing an account of a Red Colonr produced by 
mixture of a Sulphureous Spirit with a Volatile 
Atcali. 
I in making feveral Chymical Experiments found a 
Sulphureous Spirit, which being mixt with a Vola- 
tile Alcali^ fuchas Spirit of Sal Armontack, ox\Jnxi,^c, 
gives it a red Colour in a moment, and does the fame 
without any effervefcence, tho' both the Liquors were 
clear 
