The north-western frontier being invaded by the enemy, it became necessary to adopt measures for its defence. Franklin was directed by the governor to take charge of this. A power of raising men, and of appointing officers to command them, was vested in him. He soon levied a body of troops, with which he repaired to the place at which their presence was necessary. Here he built a fort, and placed a garrison in such a posture of defence, as would enable them to withstand the inroads, to which the inhabitants had previously been exposed. He remained here for some time, in order the more completely to discharge the trust committed to him. Some business of importance at length rendered his presence necessary in the assembly, and he returned to Philadelphia.
The defence of her colonies was a great expence to Great Britain. The most effectual mode of lessening this was, to put arms into the hands of the inhabitants, and to teach them their use. But England wished not that the Americans should become acquainted with their own strength. She was apprehensive, that, as soon as this period arrived, they would no longer submit to that monopoly of their trade, which to them was highly injurious, but extremely advantageous to the mother-country. In comparison with the profits of this, the expence of maintaining armies and fleets to defend them was trifling. She fought to keep them dependent upon her for protection; the best plan which could be devised for retaining them in peaceable subjection. The least appearance of a military spirit was therefore to be guarded against, and, although a war then raged, the act for organizing a militia was disapproved of by the ministry. The regiments which had been formed under it were disbanded, and the defence of the province entrusted to regular troops.
The disputes between the proprietaries and the people continued in full force, although a war was raging on the frontiers. Not even the sense of danger was sufficient to reconcile, for ever so short a time, their jarring interests. The assembly still insisted upon the justice of taxing the proprietary estates, but the governors constantly refused their assent to this measure, without which no bill could pass into a law. Enraged at the obstinacy, and what they conceived to be unjust proceedings of their opponents, the assembly at length determined to apply to the mother-country for relief. A petition was addressed to the king, in council, stating the inconveniencies under which the inhabitants laboured, from the attention of the proprietaries to their private interests, to the neglect of the general welfare of the community, and praying for redress. Franklin was appointed to present this address, as agent for the province of Pennsylvania, and departed from America in June, 1757. In conformity to the instructions which he had received from the legislature, he held a conference with the proprietaries who then resided in England, and endeavoured to prevail upon them to give up the long contested point. Finding that they would harken to no terms of accommodation, he laid his petition before the Council. During this time governor Denny assented to a law imposing a tax, in which no discrimination was made in favour of the estates of the Penn family. They, alarmed at this intelligence, and Franklin's exertions, used their utmost endeavours to prevent the royal sanction being given to this law, which they represented as highly iniquitous, designed to throw the burden of supporting government upon them, and calculated to produce the most ruinous consequences to them and their posterity. The cause was amply discussed before the privy Council. The Penns found here some strenuous advocates; nor were there wanting some who warmly espoused the side of the people. After some time spent in debate, a proposal was made, that Franklin should solemnly engage, that the assessment of the tax should be so made, as that the proprietary estates should pay no more than a due proportion. This he agreed to perform; the Penn family withdrew their opposition, and tranquillity was thus once more restored to the province.
The mode in which this dispute was terminated is a striking proof of the high opinion entertained of Franklin's integrity and honour, even by those who considered him as inimical to their views. Nor was their confidence ill-founded. The assessment was made upon the strictest principles of equity; and the proprietary estates bore only a proportionable share of the expences of supporting government.
After the completion of this important business, Franklin remained at the court of Great Britain, as agent for the province of Pennsylvania. The extensive knowledge which he possessed of the situation of the colonies, and the regard which he always manifested for their interests, occasioned his appointment to the same office by the colonies of Massachussets, Maryland, and Georgia. His conduct, in this situation, was such as rendered him still more dear to his countrymen.
He had now an opportunity of indulging in the society of those friends, whom his merits had procured him while at a distance. The regard which they had entertained for him was rather increased by a personal acquaintance. The opposition which had been made to his discoveries in philosophy gradually ceased, and the rewards of literary merit were abundantly conferred upon him. The Royal Society of London, which had at first refused his performances admission into its transactions, now thought it an honour to rank him amongst its fellows. Other societies of Europe were equally ambitious of calling him a member. The university of St. Andrew's, in Scotland, conferred upon him the degree of Doctor of Laws. Its example was followed by the universities of Edinburgh and Oxford. His correspondence was sought for by the most eminent philosophers of Europe. His letters to these abound with true science, delivered in the most simple unadorned manner.
The province of Canada was at this time in the possession of the French, who had originally settled it. The trade with the Indians, for which its situation was very convenient, was exceedingly lucrative. The French traders here found a market for their commodities, and received in return large quantities of rich furs, which they disposed of at a high price in Europe. Whilst the possession of this country was highly advantageous to France, it was a grievous inconvenience to the inhabitants of the British colonies. The Indians were almost generally desirous to cultivate the friendship of the French, by whom they were abundantly supplied with arms and ammunition. Whenever a war happened, the Indians were ready to fall upon the frontiers: and this they frequently did, even when Great Britain and France were at peace. From these considerations, it appeared to be the interest of Great Britain to gain the possession of Canada. But the importance of such an acquisition was not well understood in England. Franklin about this time published his Canada pamphlet, in which he, in a forcible manner, pointed out the advantages which would result from the conquest of this province.
An expedition against it was planned, and the command given to General Wolfe. His success is well known. At the treaty in 1762, France ceded Canada to Great Britain, and by her cession of Louisiana, at the same time, relinquished all her possessions on the continent of America.
Although Dr. Franklin was now principally occupied with political pursuits, he found time for philosophical studies. He extended his researches in electricity, and made a variety of experiments, particularly on the tourmalin. The singular properties which this stone possesses of being electrified on one side positively and on the other negatively, by heat alone, without friction, had been but lately observed.
Some experiments on the cold produced by evaporation, made by Dr. Cullen, had been communicated to Dr. Franklin, by Professor Simpson, of Glasgow. These he repeated, and found, that, by the evaporation of æther in the exhausted receiver of an air-pump, so great a degree of cold was produced in a summer's day, that water was converted into ice. This discovery he applied to the solution of a number of phenomena, particularly a singular fact, which philosophers had endeavoured in vain to account for, viz. that the temperature of the human body, when in health, never exceeds 96 degrees of Fahrenheit's thermometer, though the atmosphere which surrounds it may be heated to a much greater degree. This he attributed to the increased perspiration, and consequent evaporation, produced by the heat.