276 THE PHYSICAL GEOGRAPHY OF THE SEA. 



(§ 122), near the equator, where they produce (§ 162) the helt of 

 equatorial calms. All vessels that pass from one system of trade- 

 winds to the other have to cross this calm belt. Sometimes they 

 clear it in a few hours. Sometimes they are delayed in it for 

 weeks ; and the calm is so still and the rain so copious that the 

 fresh water is sometimes found standing in pools on the sea. 



792. If it be true, as Dove maintains, that the southwest mon- 

 soons of the Indian Ocean are the southeast trade-winds of that 

 sea pressing up toward the desert regions of Asia, then a vessel 

 bound hence to Calcutta, for instance, and entering the Indian 

 Ocean at the time of the southwest monsoon, should find no belt 

 of equatorial calms there at all, but, on the contrary, she should 

 find the southeast trade-wind to haul more and more to the south, 

 until finally, without having crossed any belt of equatorial calms, 

 she would find her sails trimmed to the southwest monsoon. 



793. In like manner, Jansen maintains that the northwest 

 monsoon is a similar deflection of the northeast trade-wind. 



794. I had many log-books relating to the Indian Ocean, and I 

 had already, at the commencement of my labors on the Wind and 

 Current Charts, essayed an examination into the monsoons of the 

 Indian Ocean, but the materials on hand at that time proved insufii- 

 cient. They have been accumulating ever since, and though not 

 yet ample enough to settle definitively such a question, they are 

 nevertheless sufficient to throw some valuable and certain light 

 upon the subject. Encouraged by Jansen, and the number of log- 

 books, I have recently put the materials in the hands of Lieuten- 

 ant West for co-ordination. 



795. The result is, tlmj give no indication of any calm belt 

 between the southeast trade-wind and the southwest nnonsoon of 

 the Indian Ocean, 



796. The Desert of Cobi and the arid wastes of Asia (§ 202) 

 are the cause of these monsoons. When the sun is north of the 

 equator, the force of his rays, beating down upon these wide and 

 thirsty plains, is such as to cause the vast superincumbent body 

 of air to expand and ascend. Consequently, there is an indraught 

 of air from the surrounding regions to supply the ascending col- 

 umn. The air that is going to feed the northeast trades is thus 



