A Treatise on Electricity Wherein its various phænomena are accounted for, and the cause of the attraction and gravitation of solids, assigned. To which is added, a — Inside the Classic

A Challenge to Newtonian Attraction

Penrose directly confronts the prevailing theory of attraction, arguing that the solidity of bodies is caused by the pressure of the air or atmosphere, not by any inherent attractive force. He cites experiments with two marble slabs that, when polished and placed together, require great force to separate—a force he attributes to the pressure of the air, since removing the air with an air pump causes them to separate immediately. He further supports this with Hauksbee's experiment using brass hemispheres, where extracting the air required 140 pounds to pull them apart. Penrose insists that if we considered that the air presseth equally every way, not just downwards, we would not have overlooked this force.

The Role of Pores and Heat

Penrose explains that the firmness of bodies depends on the make and size of their pores: bodies with smallest pores are acted upon with greater power, while those with larger pores admit light and common air. He then discusses how heat expands solids, citing the example of an iron rod that becomes bigger and longer when hot, and Boerhaave's opinion that cold consolidates firm bodies by bringing matter into a less compass. This expansion and contraction, Penrose argues, further demonstrates that cohesion is not due to attraction but to external pressure.

Electrical Attraction as Atmospheric Pressure

Having dismissed attraction and gravitation, Penrose turns to electricity to explain how heavy bodies descend toward the earth. He aligns with Hauksbee's account: if by heat and rarefaction from attrition the medium near the glass becomes specifically lighter, then the denser remoter air presses in to keep the balance—this is what we call electrical attraction. Penrose extends this reasoning to the earth's attraction, suggesting that the descent of bodies is performed in the same manner as the attraction of the glass globe in electricity. The treatise thus unifies terrestrial gravity and electrical phenomena under a single mechanical cause.

Medical Applications and the Animal Frame

The full title promises a short account of how electrical effluvia act upon the animal frame and in what disorders they may be applied with success. While the excerpts do not reveal the details of this medical section, Penrose's opening remarks indicate that great cures have been performed by random experiments, and he aims to provide a rational basis for such treatments. His background as a surgeon suggests a practical orientation, and the treatise likely applies his atmospheric theory to explain how electricity affects the body, possibly influencing conditions where the balance of internal air or pressure is disrupted.

Penrose's treatise is a tightly argued work that uses a single principle—atmospheric pressure—to account for solidity, gravity, and electrical attraction. Readers should attend to how he moves from mechanical experiments with air pumps and polished surfaces to the behavior of the glass globe, and finally to the human body. The excerpts show a writer who prizes independent thought and empirical demonstration over deference to authority, making this a revealing document of mid-18th-century scientific reasoning.

I finished Penrose's little treatise a few weeks ago and kept thinking about how he watched polished slabs cling together under a vacuum, convinced it was air's weight, not some hidden pull. That stubborn, gentle insistence reminded me of something I found later, this Bibliographical history of electricity & magnetism, chronologically arranged — Text and Context, which quietly traces all those old guesses and corrections. It felt like sitting with someone’s careful notes.