Hints to Travellers, Scientific and General, Vol. 2 / Tenth edition, revised and corrected

by Royal Geographical Society

In the Table ([pp. 44-49]), taken from Marriott’s “Hints to Meteorological Observers,” is given the relative humidity for every 2° of temperature from 20° to 80°, and for every two-tenths of a degree of difference between the dry and wet-bulb readings from 0°·2 to 18°·0.

To use the Table: Look in the column on the left or right for the nearest degree to the dry-bulb reading; then carry the eye horizontally along until the column is reached corresponding to the difference between the readings of the dry and wet-bulb thermometers, when the relative humidity will be found. Intermediate readings can be interpolated in the usual way.

Example: Dry-bulb 58°·5, wet-bulb 52°·7, the difference is 5°·8. Having found 58° in the column on the left or right, run the eye along this line until the column under 5°·8 is reached, when the relative humidity will be found, viz., 67.

Table of Relative Humidity.

Dry Bulb Reading.	Difference between the Readings of the Dry and Wet Bulb Thermometers.
	°	°	°	°	°	°	°	°	°	°	°	°	°	°	°
	0.2	0.4	0.6	0.8	1.0	1.2	1.4	1.6	1.8	2.0	2.2	2.4	2.6	2.8	3.0
°
20	93	86	80	74	68	63	59	55	51	47	44	41	37	34	32
22	94	88	82	76	70	65	60	56	53	50	47	44	41	38	36
24	94	88	83	78	73	69	65	61	57	53	50	47	44	42	39
26	95	90	85	80	76	72	68	64	61	57	54	51	48	45	43
28	96	92	88	84	80	76	72	69	66	63	60	57	54	52	50
30	96	93	90	87	84	81	78	75	72	70	67	64	62	60	58
32	97	94	91	89	87	84	82	80	78	76	73	71	69	67	65
34	97	95	93	91	89	87	85	83	81	80	78	76	74	72	71
36	98	96	94	93	91	89	87	86	84	82	80	79	77	76	74
38	98	96	94	93	91	89	87	86	85	83	81	80	78	77	76
40	98	97	95	94	92	90	88	87	86	84	82	81	79	78	76
42	98	97	95	94	92	90	88	87	86	84	83	81	80	78	77
44	98	97	95	94	92	90	88	87	86	84	83	82	81	79	78
46	99	97	95	94	92	91	89	88	87	85	84	82	81	79	78
48	99	97	95	94	92	91	89	88	87	85	84	82	81	80	79
50	99	97	96	94	93	92	90	89	88	86	85	83	82	80	79
52	99	97	96	94	93	92	90	89	88	86	85	83	82	81	80
54	99	97	96	94	93	92	90	89	88	86	85	83	82	81	80
56	99	97	96	94	93	92	90	89	88	87	86	84	83	82	81
58	99	97	96	94	93	92	90	89	88	87	86	85	84	83	82
60	99	97	96	94	93	92	91	90	89	88	86	85	84	83	82
62	99	98	96	95	94	93	91	90	89	88	86	85	84	83	82
64	99	98	96	95	94	93	91	90	89	88	86	85	84	83	82
66	99	98	96	95	94	93	91	90	89	88	87	86	85	84	83
68	99	98	96	95	94	93	92	91	90	89	87	86	85	84	83
70	99	98	96	95	94	93	92	91	90	89	87	86	85	84	83
72	99	98	96	95	94	93	92	91	90	89	87	86	85	84	83
74	99	98	96	95	94	93	92	91	90	89	88	87	85	85	84
76	99	98	97	96	95	93	92	91	90	89	88	87	86	85	84
78	99	98	97	96	95	94	93	92	91	90	89	88	87	86	85
80	99	98	97	96	95	94	93	92	91	90	89	88	87	86	85
Dry Bulb Reading.	Difference between the Readings of the Dry and Wet Bulb Thermometers.
	°	°	°	°	°	°	°	°	°	°	°	°	°	°	°
	3.2	3.4	3.6	3.8	4.0	4.2	4.4	4.6	4.8	5.0	5.2	5.4	5.6	5.8	6.0
°
20	29	27	25	23	21	19	18	17	16	15	14	13	12	11	10
22	33	31	29	27	25	23	21	19	18	17	15	14	13	12	11
24	36	34	32	30	29	27	25	23	21	19	18	17	16	15	14
26	41	39	37	35	33	31	29	27	26	25	23	21	20	19	18
28	48	46	44	42	40	38	36	34	33	32	30	29	27	26	25
30	55	53	51	49	47	45	44	42	40	39	37	36	35	33	32
32	63	61	60	58	56	54	53	51	50	48	47	45	44	42	41
34	69	67	65	63	62	60	59	57	56	55	53	52	51	50	49
36	72	71	69	68	66	64	63	61	60	59	58	57	55	54	53
38	74	73	71	70	69	67	66	64	63	62	61	60	58	57	56
40	75	74	72	71	70	68	67	65	64	63	62	61	60	59	58
42	76	75	73	72	70	69	68	66	65	64	63	62	61	60	59
44	77	76	74	73	72	71	70	68	67	65	64	63	62	61	60
46	77	76	74	73	72	71	70	68	67	66	65	64	63	62	61
48	78	77	75	74	73	72	71	69	68	67	66	65	64	63	62
50	78	77	75	74	73	72	71	70	69	68	66	65	64	63	62
52	79	78	76	75	74	73	72	71	70	69	67	66	65	64	62
54	79	78	77	76	75	73	72	71	70	69	68	67	66	65	64
56	80	79	77	76	75	74	73	72	71	70	69	68	67	66	65
58	81	80	78	77	76	75	74	73	72	71	70	69	68	67	66
60	81	80	78	77	76	75	74	73	72	71	70	69	68	67	66
62	81	80	79	78	77	76	75	74	73	72	71	70	69	68	67
64	81	80	79	78	77	76	75	74	73	72	71	70	69	68	68
66	82	81	80	79	78	77	76	75	74	73	72	71	70	69	68
68	82	81	80	79	78	77	76	75	74	73	72	71	70	69	69
70	82	81	80	79	78	77	76	75	74	74	73	72	71	70	69
72	82	81	80	79	79	78	77	76	75	74	73	72	71	70	70
74	83	82	81	80	79	78	77	76	75	74	73	72	71	70	70
76	83	82	81	80	80	79	78	77	76	75	74	73	72	71	71
78	84	83	82	81	80	79	78	77	76	75	74	73	72	71	71
80	84	83	82	81	80	79	78	77	76	76	75	74	73	72	72
Dry Bulb Reading.	Difference between the Readings of the Dry and Wet Bulb Thermometers.
	°	°	°	°	°	°	°	°	°	°	°	°	°	°	°
	6.2	6.4	6.6	6.8	7.0	7.2	7.4	7.6	7.8	8.0	8.2	8.4	8.6	8.8	9.0
°
20	9	8	7	6	6	6	5	5	5	5	..	..	..	..	..
22	10	9	9	8	8	7	7	6	6	5	5	5	5	4	4
24	13	12	11	10	10	9	9	8	8	7	7	6	6	6	5
26	17	16	15	14	14	13	12	11	10	10	9	9	8	8	7
28	24	23	21	20	19	18	17	16	15	15	14	14	13	13	12
30	31	30	29	28	28	27	26	25	24	23	22	21	20	19	18
32	39	38	37	36	35	34	33	32	31	30	29	29	28	27	27
34	47	46	45	44	43	41	40	39	38	37	36	36	35	34	33
36	52	51	49	48	47	46	45	44	43	42	41	40	39	39	38
38	55	54	52	51	50	49	48	47	46	45	44	43	42	42	41
40	57	56	54	53	52	51	50	49	48	47	46	45	44	44	43
42	58	57	56	55	54	53	52	51	50	49	48	47	46	45	44
44	59	58	57	56	55	54	53	52	51	50	49	48	47	46	46
46	60	59	58	57	56	55	54	53	52	51	50	49	48	47	47
48	61	60	59	58	57	56	55	54	53	52	51	50	49	48	48
50	61	60	59	58	58	57	56	55	54	53	52	51	50	49	49
52	62	61	60	59	59	58	57	56	55	54	53	52	51	50	50
54	63	62	61	60	59	58	57	56	55	55	54	53	52	51	51
56	64	63	62	61	60	59	58	57	56	56	55	54	53	52	52
58	65	64	63	62	61	60	59	58	57	57	56	55	54	53	53
60	65	64	63	62	62	61	60	59	59	58	57	56	55	54	54
62	66	65	64	63	63	62	61	60	59	58	57	56	56	55	55
64	67	66	65	64	63	62	61	60	59	59	58	57	57	56	55
66	67	66	65	64	64	63	62	61	60	60	59	58	58	57	56
68	68	67	66	65	65	64	63	62	61	60	59	58	58	57	56
70	68	67	66	65	65	64	63	62	61	61	60	59	59	58	57
72	69	68	67	66	65	64	63	62	61	61	60	60	59	58	58
74	69	68	67	66	66	65	64	63	62	62	61	61	60	59	59
76	70	69	68	67	66	65	65	64	63	63	62	61	61	60	59
78	70	69	68	67	67	66	65	64	63	63	62	61	61	60	60
80	71	70	69	68	67	67	66	65	64	64	63	62	62	61	60
Dry Bulb Reading.	Difference between the Readings of the Dry and Wet Bulb Thermometers.
	°	°	°	°	°	°	°	°	°	°	°	°	°	°	°
	9.2	9.4	9.6	9.8	10.0	10.2	10.4	10.6	10.8	11.0	11.2	11.4	11.6	11.8	12.0
°
20	..	..	..	..	..	..	..	..	..	..	..	..	..	..	..
22	..	..	..	..	..	..	..	..	..	..	..	..	..	..	..
24	5	5	5	5	4	..	..	..	..	..	..	..	..	..	..
26	7	6	6	6	5	5	5	5	5	4	..	..	..	..	..
28	12	11	10	10	9	9	8	8	7	7	7	6	6	6	5
30	17	16	15	15	14	14	13	13	12	12	12	11	11	10	10
32	26	25	24	23	23	22	21	20	20	19	19	18	17	17	16
34	33	32	31	30	30	29	28	27	27	26	26	25	24	24	23
36	37	36	35	34	34	33	32	31	31	30	30	29	28	28	27
38	40	39	38	37	36	35	34	33	33	32	32	31	30	30	29
40	42	41	40	39	38	37	36	35	35	34	34	33	32	32	31
42	43	42	41	40	40	39	38	37	36	36	35	34	33	32	32
44	45	44	43	42	41	41	40	39	39	38	37	36	35	34	34
46	46	45	44	43	43	42	41	40	39	39	38	37	36	35	35
48	47	46	45	44	44	43	42	41	40	40	39	38	37	36	36
50	48	47	46	45	45	44	43	42	41	41	40	40	39	39	38
52	49	48	47	46	46	45	44	44	43	43	42	41	40	40	39
54	50	49	48	47	47	46	45	45	44	44	43	42	41	41	40
56	51	50	49	48	48	47	46	46	45	45	44	43	42	42	41
58	52	51	50	49	49	48	47	47	46	46	45	45	44	44	43
60	53	52	51	50	50	49	48	47	46	46	45	45	44	44	43
62	54	53	52	51	51	50	49	48	47	47	46	46	45	45	44
64	55	54	53	52	52	51	50	49	48	48	47	47	46	46	45
66	55	54	53	52	52	51	51	50	49	49	48	48	47	47	46
68	56	55	54	53	53	52	52	51	50	50	49	48	47	47	46
70	57	56	55	54	54	53	52	51	50	50	49	49	48	48	47
72	57	56	55	54	54	53	53	52	51	51	50	50	49	49	48
74	58	57	56	55	55	54	54	53	52	52	51	50	49	49	48
76	59	58	57	56	56	55	54	53	52	52	51	51	50	50	49
78	59	58	57	56	56	55	55	54	53	53	52	52	51	51	50
80	60	59	58	57	57	56	55	54	53	53	52	52	51	51	50
Dry Bulb Reading.	Difference between the Readings of the Dry and Wet Bulb Thermometers.
	°	°	°	°	°	°	°	°	°	°	°	°	°	°	°
	12.2	12.4	12.6	12.8	13.0	13.2	13.4	13.6	13.8	14.0	14.2	14.4	14.6	14.8	15.0
°
20	..	..	..	..	..	..	..	..	..	..	..	..	..	..	..
22	..	..	..	..	..	..	..	..	..	..	..	..	..	..	..
24	..	..	..	..	..	..	..	..	..	..	..	..	..	..	..
26	..	..	..	..	..	..	..	..	..	..	..	..	..	..	..
28	5	5	5	5	4	..	..	..	..	..	..	..	..	..	..
30	10	9	9	9	8	8	7	7	7	6	6	6	6	5	5
32	16	15	15	15	14	14	13	13	13	12	12	11	11	11	10
34	23	22	21	21	20	20	19	18	18	17	17	16	16	15	15
36	27	26	25	25	24	24	23	23	23	22	22	21	21	20	20
38	29	28	27	27	26	26	25	25	24	24	23	23	22	22	21
40	31	30	29	29	28	28	27	27	26	25	25	25	24	24	23
42	31	31	30	30	29	29	28	28	27	26	26	26	25	25	24
44	33	33	32	32	31	31	30	30	29	28	28	27	26	26	25
46	34	34	33	33	32	32	31	31	30	29	29	28	27	27	26
48	35	35	34	34	33	33	32	32	31	30	30	29	29	29	28
50	37	36	35	35	34	34	33	33	32	32	31	31	30	30	29
52	38	38	37	37	36	36	35	35	34	33	32	32	31	31	30
54	39	39	38	38	37	37	36	36	35	34	33	33	32	32	31
56	40	40	39	39	38	37	36	36	35	35	34	34	33	33	33
58	42	41	40	40	39	39	38	38	37	36	35	35	34	34	34
60	42	42	41	41	40	39	38	38	37	37	36	36	35	35	35
62	43	43	42	42	41	40	39	39	38	38	37	37	36	36	35
64	44	44	43	43	42	41	40	40	39	39	38	38	37	37	36
66	45	45	44	44	43	42	41	41	40	40	39	39	38	38	37
68	45	45	44	44	43	42	41	41	40	40	39	39	38	38	38
70	46	46	45	45	44	43	42	42	41	41	40	40	39	39	38
72	47	47	46	46	45	44	43	43	42	42	41	41	40	40	39
74	47	47	46	46	45	45	44	44	43	43	42	42	41	41	40
76	48	48	47	47	46	46	45	45	44	43	43	43	42	42	41
78	49	49	48	48	47	47	46	46	45	44	43	43	42	42	41
80	49	49	48	48	47	47	46	46	45	45	44	44	43	43	42
Dry Bulb Reading.	Difference between the Readings of the Dry and Wet Bulb Thermometers.
	°	°	°	°	°	°	°	°	°	°	°	°	°	°	°
	15.2	15.4	15.6	15.8	16.0	16.2	16.4	16.6	16.8	17.0	17.2	17.4	17.6	17.8	18.0
°
20	..	..	..	..	..	..	..	..	..	..	..	..	..	..	..
22	..	..	..	..	..	..	..	..	..	..	..	..	..	..	..
24	..	..	..	..	..	..	..	..	..	..	..	..	..	..	..
26	..	..	..	..	..	..	..	..	..	..	..	..	..	..	..
28	..	..	..	..	..	..	..	..	..	..	..	..	..	..	..
30	5	5	5	4	4	..	..	..	..	..	..	..	..	..	..
32	10	10	10	9	9	9	8	8	8	7	7	7	7	6	6
34	15	14	14	14	13	13	13	12	12	12	11	11	11	10	10
36	19	19	18	18	17	17	16	16	15	15	14	14	14	13	13
38	21	20	20	20	19	19	18	18	17	17	16	16	16	15	15
40	23	22	22	22	21	21	20	20	19	19	18	18	18	17	17
42	24	23	23	23	22	22	21	21	20	20	19	19	19	18	18
44	25	24	24	24	23	23	22	22	21	21	20	20	20	19	19
46	26	25	25	25	24	24	23	23	22	21	21	21	21	20	20
48	27	27	26	26	25	24	23	23	22	22	22	21	21	20	20
50	28	28	27	27	26	26	25	25	24	24	23	22	22	21	21
52	29	29	28	28	27	27	26	26	25	25	24	24	24	23	23
54	30	30	29	29	28	28	27	27	26	26	25	25	25	24	24
56	32	32	31	31	30	29	29	28	28	27	27	26	26	25	25
58	33	33	32	32	31	31	30	30	29	29	28	28	28	27	27
60	34	34	33	33	32	32	31	31	30	30	29	29	28	28	27
62	35	34	34	33	33	33	32	32	31	31	30	30	29	29	28
64	36	35	35	34	34	33	32	32	31	31	30	30	29	29	29
66	36	36	35	35	34	34	33	33	32	32	32	31	31	30	30
68	37	37	36	36	35	35	34	34	33	33	33	32	32	31	31
70	38	37	37	36	36	35	35	35	34	34	33	33	32	32	31
72	39	38	38	37	37	36	36	35	35	34	34	34	33	33	32
74	40	39	39	38	38	37	37	36	36	35	35	35	34	34	33
76	40	40	39	39	38	38	37	37	37	36	36	36	35	35	34
78	41	40	40	39	39	39	38	38	37	37	36	36	35	35	34
80	41	41	40	40	39	39	38	38	37	37	36	36	35	35	35

Table showing the Pressure of Saturated Aqueous Vapour in inches of Mercury at Latitude 45° for each degree Fahrenheit from -30° to 119°.

°	Inch.	°	Inch.	°	Inch.	°	Inch.	°	Inches.
-30	0.0099	0	0.0440	30	0.1665	60	0.5192	90	1.4128
-29	0.0105	1	0.0461	31	0.1738	61	0.5379	91	1.4578
-28	0.0111	2	0.0482	32	0.1815	62	0.5572	92	1.5040
-27	0.0117	3	0.0504	33	0.1888	63	0.5771	93	1.5514
-26	0.0123	4	0.0527	34	0.1964	64	0.5976	94	1.6001
-25	0.0130	5	0.0551	35	0.2043	65	0.6187	95	1.6502
-24	0.0137	6	0.0577	36	0.2125	66	0.6405	96	1.7017
-23	0.0144	7	0.0604	37	0.2210	67	0.6630	97	1.7546
-22	0.0152	8	0.0632	38	0.2297	68	0.6862	98	1.8088
-21	0.0160	9	0.0661	39	0.2388	69	0.7101	99	1.8646
-20	0.0168	10	0.0691	40	0.2482	70	0.7347	100	1.922
-19	0.0177	11	0.0723	41	0.2579	71	0.7601	101	1.980
-18	0.0186	12	0.0756	42	0.2679	72	0.7862	102	2.041
-17	0.0196	13	0.0790	43	0.2783	73	0.8131	103	2.103
-16	0.0206	14	0.0825	44	0.2890	74	0.8409	104	2.166
-15	0.0217	15	0.0862	45	0.3001	75	0.8695	105	2.231
-14	0.0228	16	0.0901	46	0.3116	76	0.8989	106	2.298
-13	0.0239	17	0.0942	47	0.3235	77	0.9292	107	2.366
-12	0.0251	18	0.0985	48	0.3358	78	0.9604	108	2.437
-11	0.0263	19	0.1030	49	0.3485	79	0.9925	109	2.509
-10	0.0276	20	0.1076	50	0.3616	80	1.0255	110	2.583
- 9	0.0289	21	0.1124	51	0.3751	81	1.0595	111	2.659
- 8	0.0303	22	0.1174	52	0.3891	82	1.0945	112	2.736
- 7	0.0318	23	0.1226	53	0.4036	83	1.1305	113	2.817
- 6	0.0333	24	0.1282	54	0.4186	84	1.1675	114	2.898
- 5	0.0349	25	0.1339	55	0.4341	85	1.2056	115	2.982
- 4	0.0366	26	0.1399	56	0.4501	86	1.2447	116	3.067
- 3	0.0383	27	0.1461	57	0.4666	87	1.2850	117	3.156
- 2	0.0401	28	0.1526	58	0.4836	88	1.3264	118	3.246
- 1	0.0420	29	0.1594	59	0.5011	89	1.3690	119	3.338

Transcriber’s Note: Maps are clickable for larger versions.