691. The barometric descent of the monsoons.—Each monsoon, like the trade-winds, blows from a higher to a lower barometer. Taking tip the clew from this fact, and resorting again to the graphic method for illustration, we may ascertain, with considerable
accuracy, not only the relative strength of the north-east and south-west monsoons of the sea, but also the mean height of the barometer in the interior of India during the south-west monsoon, supposing that monsoon to go no farther than the mountain range, which may be taken at a mean to be about the parallel of 30° north. Now, taking the mean height of the barometer at the equatorial calm belt to be (§ 362) 29.92 inches; the mean height in the calm belt of Cancer to be 30.21 inches, the line N.E. of the Diagram D will represent the average barometric declivity of the north-east monsoons generally. The mean height of the barometer during the three months of June, July,
