As before intimated, the public ways are mainly for the use of travellers; but in the progress of civilization it has become convenient and necessary to use them for other purposes of a public nature. It is the great merit of the common law, that while its fundamental principles remain fixed from generation to generation, yet they are generally so comprehensive and so well adapted to new institutions and conditions of society, new modes of commerce, new usages and practices, that they are capable of application to every phase of society and business life. Time and necessity, as well as locality, are important elements in determining the character of any particular use of a public way. Many public ways are now used for gas, water-pipes, and sewers, because the public health and convenience are subserved by such use.[57] They are also used for the transmission of intelligence by electricity, and the post-boy and the mail-coach are disappearing. [57] 35 N.H. 257. The horse-railroad was deemed a new invention; but it was held that a portion of the road might well be set aside for it, although the rights of other travellers to some extent were limited by the privileges necessary for its use.[58] [58] 136 Mass. 75. And now motor cars and elevated railroads are making their appearance in the centres of civilized life, and the bicycle and tricycle are familiar objects on all the great thoroughfares. Should human ingenuity discover any new modes of conveying persons and property over the public ways, or of transmitting intelligence along the same, which should prove convenient to the everyday life of humanity, no doubt the highway law will be found applicable to all the needs of advancing civilization. The underlying principle of the law is that every person may use the highway to his own best advantage, but with a just regard to the like rights of others. The law does not specify what kind of animals or vehicles are to be allowed upon the road, but leaves every case to be decided as it shall arise, in view of the customs and necessities of the people from time to time. All persons may lawfully travel upon the public ways with any animal or vehicle which is suitable for a way prepared and intended to afford the usual and reasonable accommodations needful to the requirements of a people in their present state of civilization; but if any person undertakes to use or travel upon the highway in an unusual or extraordinary manner, or with animals, vehicles, or freight not suitable or adapted to a way opened and prepared for the public use, in the common intercourse of society, and in the transaction of usual and ordinary business, he then takes every possible risk of loss and damage upon himself.[59] [59] 14 Gray, 242.