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Object Overview
This Pendant Thermometer with Bloodstone, made in the United States around 1910–1920, is a mass-produced novelty, assembled by an anonymous workshop from a bought-in movement and bought-in findings. The pendant is a small fragment of a large and largely forgotten fashion of the turn of the nineteenth and twentieth centuries — the vogue for wearable miniature instruments, when thermometers, compasses, tiny aneroids and weather forecasters were hung from the watch chain alongside seals and lockets. To wear a thermometer on one's chest was to declare allegiance to the age of measurement: I am a modern man, I trust the number rather than the omen.
The instrument is housed in a round, double-sided case suspended from a rigid bail soldered to the rim. There is no swivel — this is not a "spinner": the pendant hangs freely and, in wear, turns to show first one face and then the other. Both sides are finished as display faces, which for an object of this genre is precisely the point.
n/a
bi-metallic
brass, copper, glass, paper, steel, stone
The overall diameter, bezel included, is 24 mm. Around the perimeter runs a wreath of beads — the so-called cannonball or beaded bezel, an old and thoroughly jeweller's device: the same ring of soldered hemispheres was also made in gold, and is here reproduced in a base metal.
The metal is a warm golden tone with a distinct rosy cast in the highlights on the crowns of the beads. This is characteristic of tombac, a high-copper brass that gave the look of gold without the gold. The identification rests on colour and the character of the patina and has not been confirmed by analysis of the composition; in the hollows between the beads the metal has darkened to brown, while the crowns are rubbed to a lighter tone — the usual pattern of wear for copper alloys.
The reverse is closed by a polished disc of heliotrope (bloodstone), a variety of green chalcedony-jasper, set flush into the bezel. The colour is a deep dark green with a fine sub-parallel fibrous banding; scattered across the field are pale grey cloudy patches with diffuse edges and sparse rusty-brown specks. The red inclusions that give the stone its name are only weakly expressed here.
The stone scratches window glass and is inert under 365 nm UV. This places its hardness in the range of 6.5–7 and rules out serpentine, which it can closely resemble. The matt, pale areas are zones where the polish has been lost.
The disc is left plain, without carving or engraving. It is the standard blank awaiting a monogram that its owner never ordered — and at the same time a memory of the fob seal from which the whole genre grew.
A long neck chain: opera length (84 cm), faceted cable links, barrel clasp — a faceted cable link of square section, with a clasp formed of a hollow cylinder and a tapered pin with an eye. It is worn at full length and passes freely over the head.
The dial is printed paper laid on a metal backing disc. The tone is a warm cream with uneven yellowing and staining; the lettering and graduations are lithographed, with varying density of ink.
The scale is concentric and calibrated in degrees Fahrenheit over a range of −30 to +140 °F. The graduation occupies almost the full circumference: the zero mark stands at the bottom centre, the negative branch runs off to the right and the positive branch to the left and then over the top to the right-hand edge, where the upper end of the scale very nearly meets the lower. Two small curved arrows at the bottom, flanking the inscription, mark this junction and the direction of the two branches.
The dial is protected by a flat mineral glass with a bevelled edge. The pointer is tiny but elegantly made, of blued steel.
At the bottom of the dial is printed PAT. APLD. FOR — the American abbreviation of Patent Applied For: an application had been filed, but the patent had not yet been granted when the dial was printed. The spelling "APLD" is characteristic of the United States and serves as indirect evidence of origin.
The marking carried no legal force: until a patent issued, its holder could neither prohibit copying nor recover damages. It functioned as a warning to competitors — the ground is staked — and, on inexpensive novelty goods, as a badge of "invention" that lent the article weight in the buyer's eyes.
No inventor's name, application number or date appears, and so the patent — if one was ever granted — cannot be identified; it is not even known what was being patented: the movement, the method of securing the disc, or the mount itself. Manufacturers normally replaced such a marking with the patent number once the patent issued, which places manufacture between filing and grant. On cheap goods, however, printing plates were often left unchanged, and the absence of a number does not prove that no patent was granted.
At the heart of the instrument is a bimetallic spiral: a strip of two bonded metals with different coefficients of thermal expansion, coiled into a flat spiral. The outer end is anchored in the case, the inner end sits on the arbor of the pointer. On heating, the layer with the greater expansion lengthens more, the spiral winds tighter, and the pointer travels across the scale; on cooling the process reverses.
The principle was worked out as early as the eighteenth century by watchmakers, in the compensation balances of chronometers, and it dispenses with any liquid: the instrument is flat as a coin, indifferent to its orientation and unafraid of shaking. The price is modest accuracy and appreciable thermal lag.
Hence the manner of use built into the design: the range of the scale is that of air, not of the body, so an instrument pressed against the chest would read its owner's temperature. It was meant to be read held up by its chain, free in the air, after a minute or two had been allowed for the reading to settle.
This Pendant Thermometer is a document of that brief moment when the precision instrument came down from the laboratory shelf onto the chest and became a matter of fashion; when measuring the temperature of the air about one’s person was part practice, part the pose of the technophile. The fashion faded quickly, and for obvious reasons. The First World War moved the watch from the chain to the wrist, and the waistcoat ecosystem of pendants was orphaned. Radio brought the weather forecast into every home — there was no longer any point in wearing a forecaster on one’s chest. The motor car and the aeroplane claimed the aneroid for themselves, turning it into the onboard altimeter: the instrument left the person once again, this time in favour of the machine. By the 1930s the pendant thermometer was already a curiosity from grandmother’s jewellery box.
What remains is a nameless trinket of twenty-four millimetres — with a bimetallic spiral inside, a stone awaiting a monogram that nobody ever ordered, and the promise of a patent that may never have existed.