Within the past four years we have distributed the sum of $3,700, in prizes for the largest lists of subscribers furnished according to certain prescribed limits. Previous to entering upon this system of awarding prizes, we depended principally on tried friends and canvassing agents to keep the circulation of the Scientific American upon a steadily increasing basis. ^ We have never been disappointed in our friends, but we were cheated, and the pubitc were swindled, by a few unprincipled agents who took money for our paper and never remitted it to us. To save ourselves from suspicion, and the public from being wronged we renounced the system and resorted to one of offering prizes, which has been thus far most satisfactory. Within the next six weeks we must arrange our plans for the new volume which will begin on Sept. 11. We are anxious that the circulation of the j Scientific American should be largely increased, and we wish to secure this object in the best and most unexceptionable manner. We are now engaged in maturing some plan for the campaign, and we present this brief statement for the purpose of eliciting an expression of opinion from our subscribers. We would like to receive an immediate response in writing from all those who propose to enter the field of competition, in case we should offer prizes upon about the same scale of last year, ranging in sums from $20 to $300. If these responses are promptly made and are of an encouraging nature, we shall announce within a few weeks a list so that all may begin the competition in good time to commence the next volume. The yearly subscription on all clubs above 20 names will be only $1 40. Mists.—The formation of mists never takes place if the temperature of the water be lower than that of the atmosphere; but when the cold air above the land mixes with the warmer air above the water, mist or fog will be the result, which will be so much the greater in quantity as the land surrounding the water is higher and deeper. It is by the deposition of water from the atmosphere, through the operation of this law, that the mountains ^nd plains in hot climates are covered with verdure and fertility. ^