[ 5 3 
Arithmetic has always been allowed upon no more 
certain a Foundation. 
SECT. II. 
A View of the Machines in generaL 
' | 'HE Machines neceffary to the making Obferva- 
tions for a 'Diary of the JVeather , are thefe five i 
1. The Barometer. 
I have found thofe with open Cifterns more fenfi* 
ble than the portable ones. That with which I make 
my Obfervations, is with an open Ciftern , furnifh’d 
with a Micrometer , that divides an Inch into 400 
Parts } by which I am capable of perceiving the moft 
minute Alteration of the Gravity of th zAir'. It was 
made by Mr. Bird of the Strand ; whofe Accuracy 
in Graduation deferves, I think, Notice and Encou- 
ragement. 
2. The Thermometer. 
Mine is one made by Fahrenheit's Scale on one 
Side, with its Correfpondence to the Graduation of 
the Alcohol Thermometer on the other. 
Of the three next Machines , two are new , and 
the other confiderably altered, and, 1 hope, improved, 
from one offered to the Society a great while ago. 
Note , All the Machines, except the Barometer, are 
expofed to the open Air. The Thermometer 
and Hygrometer are placed in a little Shed ? 
made for their Reception, againft my Study - 
Window , where I can fee the Graduation thro’ 
the Glaft; and, by lifting up the Safh, can, take 
them in, as Occafion requires. 
SECT. 
