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
![](http://upload.wikimedia.org/wikipedia/commons/thumb/2/2c/P370_Diagram_C.jpg/300px-P370_Diagram_C.jpg)
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,