1 83 Trcatife an Time-pteces. 



Chapter VI. treats of the compenfation for temperature produced by the balance itfelf. 

 In the feventh chapter, cit. Berthoud gives the conftrudtion and means of executing a port- 

 able watch, the compenfation of which is produced by the balance and the pendulum fpring. 

 And, laftly, he explains the conftruftion of a vertical watch, without a fufee, and carried by 

 fufpenfion. A method is given to remedy the want of ifochronifm in the pendulum fpring by 

 means of the balance iifelf. 



The fecond volume of this work is entitled, Suite duTraite des Montres a Longitudes, &c, or 

 Supplement to the Treatife on Time-pieces, containing the conftrudlion of portable vertical 

 watches (montres), and of horizontal time-pieces (horloges), for the longeft voyages: the de- 

 fcription and trials of fmall horizontal * watches, very fimple and portable ; with two engraved 

 plates. Paris, in the 5 th republican year. 



This volume, which has been printed a year, has not yet been announced or publiflied. It 

 is divided into two parts. Citizen Berthoud, in the firfl place, treats of the queftion of the 

 beft pofition for portable watches, and fmall time-pieces. In the next place, he treats of the 

 moft convenient number of vibrations of the balance, to diminifh the fridlions, and render the 

 watch moft convenient for the obferver. He defcribes the conftruftion of the balance, which 

 bears its own compenfation ; the moft fimple and fure conftruflrion of the free efcapement, and 

 the fpiral fprings of watches to render the vibrations of the balance ifchronal ; the defcription of 

 the elaftic balance, ferving for the meafure and proof of the fpiral fprings j and, laftly, he ex- 

 plains the method of trying time-pieces. 



In the fecond part, we find the conftrudlion of the vertical watch, no. 56. — the portable vertical 

 watches, no. 60 and 62 ; — of the fmall horizontal time-piece, no. 63. conftrudled to give the 

 longitude in the longeft voyages ; — of the fmall horizontal time-piece, no. 66. without (rouleau). 

 And in the conclufion the author treats of vertical watches, and fmall horizontal time-pieces. 

 The author gives the preference to the latter. 



This work is terminated by a fupplement, containing the refult of the trials made with the 

 horizontal watch, no. 65. in which the pivots of the balance turn fimply in holes made in 

 copper (cuivre) ; and, laftly, we find the conftruclion of a very fimple portable watch, and of 

 a fmall horizontal time-piece improved from no. 65. 



In the efTay on weights and meafures, the author gives the dimenfions of a cylindrical pendu- 

 lum, vibrating on knife edges, reprefenting the French foot, and the refults of trials made in 

 1791, to determine the ofcillations, which proved to be 7710 per hour. Though the pendulum 

 has been abandoned, in order to fubftitute the ten-millionth part of the quadrant of the meridian, 

 yet the labours of citizen Berthoud to preferve the dimenfions of any determinate pendulum, 

 cannot be viewed without intcreft. 



Upon the whole, this new work is calculated to add to the reputation of its illuftrious author, 

 and exhibits, without myflery, thofe pracSices which have procured him repeated fuccefs in his 

 marine time -pieces, of which the produftion is of fo much importance to navigation. 



* I fuppofe the words horizontal and vertical in the who'e of this account, to relate merely to t! e pofition in 

 which the time-pitce is to be habitually kept, and not to he nature of thsir escapements. The word hori^omal 

 has not, I believe, been applied to any efcapemeut by tiie French. N. 



