FROM OUR VOLUNTEERS Camp Tennelly (Washington, DC), August 11, 1861 Within the past few weeks the Cambria Guards have dispensed with the Camp Wright past times and amusements and are beginning to play the soldier in dead earnest. We are now encamped about six miles from Washington, up the Potomac river, on an open, elevated piece of ground. The location is quite a pleasant one.  A small stream of water meanders by in close proximity, furnishing us with the wherewithal to do our washing, etc. We are also blessed with excellent drinking water.  It is extremely warm here, but by no means unhealthy. The effect of the heat in this climate is altogether different from that on the mountain; for I find that the hotter the weather the healthier it is.  The 11th regiment has had its turn on picket. We started out on Friday evening and returned to camp at 8 P.M. on Saturday. Co. A. guarded about a mile and a half of road. None of the pickets were in any way disturbed, and we returne...