With this glance at the surroundings of Mackinac, the following table of altitudes will appropriately close the chapter. It is drawn from Professor Winchell's Geological Report for 1860:

CHAPTER X.

MACKINAC AS A HEALTH RESORT.

MACKINAC as a health resort is unsurpassed.

Its cool air and pure water, together with its natural beauties and historic associations, are just what are needed to bring back the glow of health to the faded cheek, and send the warm currents of life dancing through the system with youthful vigor.

In Mackinac, you eat with a new relish, and sleep as when a child. You row, you ramble like boys and girls, scarcely able to keep your buoyancy within bounds. You need to set a double guard about your dignity, lest it escape you entirely. But it is unnecessary for us to bear testimony on this subject, when so many more competent witnesses are at hand.

The following letter by Dr. Mills, A. A. Surg., U. S. A., shows the philosophy of the health-restoring circumstances which surround the invalid on this island:

FORT MACKINAC, MICH., May 2, 1870.

Rev. Jas. A. Van Fleet:

DEAR SIR,-In complying with your request for my views on Mackinac as a resort for invalids, I will be as brief as possible. I have been a resident upon the island during the period of nearly three years, engaged in civil and military practice, and therefore have had something of an opportunity for forming an opinion upon that subject.

In the first place, there are two governing ideas in the selection of places of resort for those in ill health. If possible that locality should be sought which will most probably be the means of a permanent cure. When such a result is beyond

ance.

hope, the present comfort of the patient stands next in importThat place, therefore, which affords the greatest number of health-giving and comfort-giving elements, will meet the wants of the largest class. But no single locality can be expected to meet the wants of all. No land of bliss, where joys are unalloyed, has as yet been discovered. There are certain places adapted to the wants of particular cases. In the selection of these, accurate knowledge and sound judgment should be the constant guides. The hurly-burly, hap-hazard manner in which people post off to some celebrated locality, in search of health, is an illustration of the kind of reasoning almost unconsciously employed by many, who upon other subjects are considered sound thinkers: the old doctrine over again, "What's good for one thing must be good for another." Hence the crowds which throng the springs and the wells, all undergoing the same internal and external drenchings, in the endeavor to cure almost as many different diseases as there are people on the grounds. There is undoubtedly much benefit to be derived from the judicious use of water. No one will deny that the springs of the country are the sources of many blessings. Yet many weak, debilitated, half dead men, women and children have had the last sparks of vitality drowned out of them, in the blind routine of water cure; while others with good constitutions, who only needed a thorough cleansing of the cutaneous surfaces, which they should have had at home, for decency's sake, have returned to the bosom of their families rejoicing in the wonderful efficacy of the springs. I have no word of condemnation for the springs. I do not deny the medicinal qualities of many of them. But the absurdity of the manner in which they are resorted to, without competent advice, and often to the actual injury of those fondly seeking a cure, must be obvious to all.

Mackinac is available as a place of resort for health and pleasure at present only in summer; but the time is not far distant when it will be as noted as a resort for invalids in winter as it is now in summer.

Its position geographically and hydrographically is such as to render the temperature at all seasons of the year moderate and uniform. This is the first and most important in the list of health-restoring and health-preserving influences to be enumerated in connection with this place. This is the central fact, around which all the others arrange themselves. It is in the mildness and uniformity of its temperature that the superiority of Mackinac as a place of resort exists. It is this that causes thousands to come here annually to spend the "heated term." This is well shown by an examination of the following table:

DEGREES OF MEAN, MONTHLY, AND EXTREME TEMPERATURE, FOR A SERIES OF YEARS.*

* Climatology of United States, by Lorin Blodget: 1857.

By this table it will be seen that the extremes of heat and cold are not only not as great in Mackinac as in other places east and west on the same parallel, but even in places much farther south. At Montreal, during the time embraced in the table, the mercury has been as low as 36 degrees below zero, and as high as 102 above. At St. Paul, on nearly the same parallel, the greatest degree of cold designated is 37 degrees below zero, and of heat, 100 above. At St. Louis, hundreds of miles farther south, the table shows that the mercury has been as low as 25 degrees below zero, and as high as 108 above. By looking at the figures opposite Mackinac, it will be

seen that 23 degrees below zero is the lowest, and go above the highest mark of the mercury. During my residence here, however, the mercury has but once been as low as 19 degrees below zero. This was during the winter of 1867 and 1868. During the winter of 1868 and 1869, 16 degrees below zero was the coldest. During the past winter 13 degrees below occurred but once.

Why this difference in favor of Mackinac? In my opinion it is owing principally to the influence of the large bodies of water which surround it; Lake Superior on the north-west, Huron on the east and south, and Michigan on the south and west. By a well known law in physics, heat is absorbed or rendered latent in the passage of any substance from the solid to the fluid and from the fluid to the gaseous states; and conversely, heat is given out or rendered sensible in the passage of any substance from the gaseous to the fluid, and from the fluid to the solid states. To illustrate: Take a single pound of ice. The thermometer shows its temperature to be 32 degrees Fahrenheit. Now, if just enough heat be applied to this pound of ice to change it from the solid to the fluid state, and the temperature of the water thus produced is immediately tested, it will be found to be only 32 degrees F., the same as found in testing the temperature of the ice before the application of heat. Here has been an expenditure of heat in the process of liquefaction. By accurate measurement it has been found that 140 degrees of heat are necessary for this change from ice to water. If, again, heat is applied to this water, the temperature will contirue to rise until it reaches 212 degrees, the ordinary boiling point of water. But all attempts to heat this water above that point will be in vain. Why? Because heat is necessary for the transformation of water into steam, and every degree of heat which is now added will be consumed or rendered latent in this process. The reverse process is naturally attended by the opposite result. Hence the philosophy of the warming of buildings by steam. Wherever the steam comes in contact with objects sufficiently cold to reduce