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Explanation of Rain Gauge, Summer 1809

From Daily Record, 1 November 1802-25 May 1826 (Massachusetts Historical Society).

In Jefferson’s hand in available spaces in margin alongside entries for June-August 1809.

I shall begin with the next month to use my rain gauge. The diam. of it's tube is <.9875 I. that of the glass funnel 3.255 consequently as 3.2552 : .9752 or as> .9875 I. that of the glass funnel is 3.2187 consequently as 3.21872 : .98752 or as 10.36 : .975 :: <so is the depth of water in the graduated tube : to the depth fallen> so is the area of the funnel to the area of the tube & so is the depth of water in the tube to the depth fallen on the earth. <therefore the depth in the tube divided & .975 : 10.36 : : 10.87 therefore the depth in the tube divided by 10.87 = the depth fallen. The tube being but 7. I. deep will be filled by a fall of .644 I. of rain. The area of the mouth of the tube is to the area of the tube as 2.066 : .975>

the diam. of the tube of the rain gage being .9875 & that of it’s mouth 1.4375 I. the square of 1.4375 will be to that of .9875 or 2.066 : .975 as the height of rain in the tube to that fallen on the ground. then in the tube

.1 =.0471
.2 =.0943
.3 =.1415
.4 =.1887
.5 =.2358
.6 =.2830
.7 =.3302
.8 =.3774
.9 =.4245
1. =.4717

 

the diam. of the tube of the rain-gage being .9875 & that of the small glass funnel <exactly double to wit [...]> 2. I the height of water in the tube will be <exactly 4 times> to that fallen on the earth, to wit

.1 =.02437
.2 =.0487
.3 =.0731
.4 =.0975
.5 =.1218
.6 =.1462
.7 =.1706
.8 =.195
.9 =.2193
1. =.2437
1. =.2437
2. =.4875
3. =.7312
4. =.975
5. =1.2187
6. =1.4625
7. =1.7062
8. =1.95
9. =2.1937

 

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