The fact that the British Association meets this year in Canada gives unusual interest to the meeting of the American Association for the Advancement of Science at Philadelphia, from September 4 to 11. After the Montreal meeting those who feel inclined can make their way leisurely to Philadelphia where it is evident from the information before us, they will meet with a warm reception. On the Friday evening, September 5, after the address of the retiring president (Professor C. A. Young, of New Jersey) a general reception will be tendered by the citizens and ladies of Philadelphia to the members of the British and American Associations, and the ladies accompanying them. The British Association has been cordially invited, both by the American Association to take part in the proceedings, and by the local committee representing the citizens of Philadelphia, to accept the warm welcome which will be tendered them during the joint session. The local committee has, indeed, been divided into a number of subcommittees for the sole purpose of rendering the stay of their visitors agreeable It will, therefore, only be courteous on the part of Britons who intend to be present at the American meeting to comply with the committee's request, and send their names, together with the number of ladies and gentlemen in their parties, as early as possible, to Dr. Persifor Frazer, 201, South Fifth street, Philadelphia. During the week occupied by the session there will be a number of receptions, entertainments, and excursions, and a day will be set apart for the examination of the International Electrical Exhibition, to be held at Philadelphia under the auspices of the Franklin Institute, and commencing September 2. By an arrangement between the Canadian and United States Trunk lines, members of the British Association will be conveyed between Montreal and Philadelphia at specially low fares, while the hotel charges at the latter city during the meeting are not expected to exceed three dollars a day. We believe the number who have already promised to be at the Montreal meeting is about seven-hundred and fifty, so that with those who will go without promising, added to the many Canadian and United States scientists who are sure to be present, the meeting is likely to be in numbers more than an average one. Letter No. 4. _September 17th, Toronto, The "Chestnuts."_