With regard to the tenth book, there can be no doubt that its hymns came into being at a time when the first nine already existed. Its composers grew up in the knowledge of the older books, with which they betray their familiarity at every turn. The fact that the author of one of its groups (20-26) begins with the opening words (agnim ile) of the first stanza of the Rigveda, is probably an indication that Books I.-IX. already existed in his day even as a combined collection. That the tenth book is indeed an aggregate of supplementary hymns is shown by its position after the Soma book, and by the number of its hymns being made up to that of the first book (191). The unity which connects its poetry is chronological; for it is the book of recent groups and recent single hymns. Nevertheless the supplements collected in it appear for the most part to be older than the additions which occur in the earlier books. There are many criteria, derived from its matter as well as its form, showing the recent origin of the tenth book. With regard to mythology, we find the earlier gods beginning to lose their hold on the imagination of these later singers. Some of them seem to be disappearing, like the goddess of Dawn, while only deities of widely established popularity, such as Indra and Agni, maintain their position. The comprehensive group of the Viçve devas, or "All gods," has alone increased in prominence. On the other hand, an altogether new type, the deification of purely abstract ideas, such as "Wrath" and "Faith," now appears for the first time. Here, too, a number of hymns are found dealing with subjects foreign to the earlier books, such as cosmogony and philosophical speculation, wedding and burial rites, spells and incantations, which give to this book a distinctive character besides indicating its recent origin. Linguistically, also, the tenth book is clearly distinguished as later than the other books, forming in many respects a transition to the other Vedas. A few examples will here suffice to show this. Vowel contractions occur much more frequently, while the hiatus has grown rarer. The use of the letter l, as compared with r, is, in agreement with later Sanskrit, strikingly on the increase. In inflexion the employment of the Vedic nominative plural in asas is on the decline. With regard to the vocabulary, many old words are going out of use, while others are becoming commoner. Thus the particle sim, occurring fifty times in the rest of the Rigveda, is found only once in the tenth book. A number of words common in the later language are only to be met with in this book; for instance, labh, "to take," kala, "time," lakshmi, "fortune," evam, "thus." Here, too, a number of conscious archaisms can be pointed out.