[29] This constant logarithm contains the reduction of the diff. of longitude to parts of radius unity, and to _Briggs_’s Modulus. [30] See _Cotesii_ Logometr. prop. 6. [31] Physiological Essays, p. 69. [32] Physiological Essays, p. 69. [33] Dr. Pringle’s Observations on the Diseases of the Army, part iii. chap. 2. [34] Vincentius Menghinus _de Ferrearum particularum progressu in Sanguinem. Comment. Acad. Bonon._ T. II. P. 2. pag. 475. [35] Phil. Transact. by Lowthorpe, vol. iii. p. 102. edit. 1749. the same by Jones, vol. v. p. 259. [36] Vol. I. art. xii. p. 364. [37] In a paper read Feb. 24. 1757. See Art. xiii. p. 88. [38] _Porticuum, in quibus spatiari consueverat (Domitianus) parietes phengite lapide distinxit, e cujus splendore per imagines quicquid a tergo fieret, provideret._ Sueton. Domit. c. 14. [39] Plin. Nat. Hist. lib. xxxvi. c. 26. §. 66. [40] Pliny mentions a kind of glass or jet called _obsidianum_: --_nigerrimi coloris, aliquando et translucidi, crassiore visu, atque in speculis parietum pro imagine umbras reddente_. Nat. Hist. lib. xxxvi. c. 26. §. 67. And that the practice of staining glass was known in his time, appears from what he says concerning the _obsidianum_ mentioned above:--_Fit et genere tincturæ--totum rubens vitrum, atque non translucidum_. Ibid. [41] Panciroll. Rer. Mem. p. 288. [42] These glass balls had sometimes water within them: _Cùm additâ aquâ vitreæ pilæ sole adverso in tantum excandescant, ut vestes exurant_. Plin. lib. xxxvi. c. 22. §. 45. _Invenio medicos, quæ sunt urenda corporum, non alitèr utilius id fieri putare, quam crystallinâ pilâ adversis positâ solis radiis._ Plin. Nat. Hist. lib. xxxvii. c. 6. §. 10. [43] Vid. Mons. Renaudot Memoires de l’Acad. des Inscript. tom. I. [44] Vid. infra, not. 11. [45] _Theatrum Scauri_----_scena ei triplex in altitudinem_ CCCLX _columnarum_.----_Ima pars scenæ e marmore fuit_: media e vitro: _summa e tabulis inauratis_. Nat. Hist. lib. xxxvi. c. 15. [46] A. V. 678. Hard. not. Plin. lib. xxxvi. c. 8. [47] _Agrippa in thermis, quas Romæ fecit, figlinum opus encausto pinxit, in reliquis albaria adornavit: non dubiè_ vitreas facturus cameras, si prius inventum id fuisset, _aut a parietibus scenæ--Scauri pervenisset in cameras_. Lib. xxxvi. c. 25. §. 64. [48] Seneca, exposing the luxury of the Romans with regard to their baths, says, _Pauper sibi videtur ac sordidus, nisi parietes magnis ac pretiosis orbibus refulserint--nisi_ vitro absconditur camera.--Ep. 86. [49] Plin. Nat. Hist. lib. xxxvi. c. 22. §. 45. [50] Nat. Hist. lib. xxxvi. c. 22. §. 45. [51] Vid. Salmasius in a passage to be produced hereafter. [52] Hist. de l’Acad. des Inscrip. tom. I. [53] Montfauc. Antiq. vol. III. part i. lib. iii. c. 4. Lipsius in loc. _&c._ [54] _Quædam nostrâ demum prodiisse memoriâ scimus; ut speculariorum usum, perlucente testâ, clarum transmittentium lumen._ Sen. ep. 90.