The proportion of mounted troops in an army varies according to the nature of the country which is the theatre of military operations. In a level country it should be about one fourth or one fifth, while in one that is mountainous, it should not be greater than a tenth. As a general rule, improvements in firearms have produced a decrease in the proportion of cavalry and lessened its importance. When artillery was introduced, the cavaliers, who composed the Middle Age armies exclusively, commenced to disappear; knighthood passed out of existence, being superseded by mercenary bands. Infantry gradually assumed importance, which has constantly increased, until it has now attained the vast predominance. This has not only caused a general diminution of the proportion of cavalry, but has entailed on the Governments of Europe the necessity of keeping their cavalry service always at its maximum, so that the mounted troops may be perfect in their drill; whereas infantry troops can acquire comparative proficiency in a few months. We will give a brief description of the different classes of cavalry, and close our subject by some remarks on the operation of this arm of service in our civil war. The regiments raised by Prince Maurice, of Orange, above referred to, were the first known as _cuirassiers_, on account of the cuirasses which they wore for defence. All defensive armor is now being laid aside. _Dragoons_ originally were a class of soldiers who operated both on foot and mounted. They are supposed to take their name from a kind of firearm called a 'dragon.' In modern practice dragoons are almost entirely used as cavalry, and rarely have recourse to any extended service on foot. The denomination 'dragoons' has recently been abolished from our service. _Carabineers_ were at first some Basque and Gascon horsemen in the French service, whose peculiarly distinguishing characteristic was a skilful use in the saddle of a short firearm. _Hussars_ originated in Hungary, taking their denomination from the word _husz_, which signifies twenty, and _ar_, pay--every twentieth man being required by the state to enter into service. From their origin they were distinguished for the celerity of their movements and their devotion to fine costumes. The _hulans_ were a species of Polish light cavalry, bearing lances, and taking their name from their commander--a nobleman named Huland. _Chasseurs_ are French regiments, designed chiefly to act as scouts and skirmishers. The _chasseurs d'Afrique_ are cavalry which have been trained in Algeria, and have become exceedingly expert through conflicts with the Arabs. The _spahis_ are Arab cavalry, in the French service, and are such admirable riders that they will charge over all kinds of ground, and dash upon a foe who judges himself secure amid rocks or trees or ditches.