One very common illusion employed in theaters, museums, shows and other venues is Pepper’s Ghost. The illusion is named after English scientist John H. Pepper who improved upon a previous ingenious but cumbersome illusion developed by inventor Henry Dircks in 1860. Pepper made the first demonstration of this illusion in 1862. The illusion relies on the fact that whereas light goes through most transparent glasses, a certain percentage of it is reflected by the surface of the glass. In the classical Peppers Ghost illusion, a glass is installed at an angle facing an audience. The audience can see with no problem the action taking place in the stage behind the glass. At some point an actor or an object is illuminated in a compartment that is located to the side of the glass in such a way that the light coming from the actor or object will bounce off the glass and appear to the audience to be coming from the stage as a ghostly apparition.
In the photo below, I use a window to generate a version of the Pepper’s Ghost illusion, where I seem to be within the tree outside as a ghostly apparition.
In the video I used an exhibit at the 2019 Prague Quadrennial. I manipulated the see-through and reflection qualities of the glass window of the exhibit as well as the proximity of my phone to the glass, to create a Peper’s Ghost illusion.
Note: the photo belongs to the author and can only be used with permission.
I woke up one day to gnawing sounds in the attic right above my bed. For the next few days these sounds continued and became very bothersome making it difficult to sleep. Science Cat heard them too. She would stand on her hind legs with her front legs against the wall and look at the ceiling. I suspected we had a squirrel up there. Squirrels are mammals which belong to the order Rodentia. These also include rats, mice, chipmunks, beavers, and porcupines.
One defining characteristic of rodents is that they have pairs of sharp incisor teeth in their upper and lower jaws which grow continuously throughout their lives. As a result of this, rodents need to gnaw very often, even if they are not eating, to wear down their teeth. If they don’t do this, their teeth can grow so large that it can kill them by making eating problematic and even piercing the palate of their jaws. Because of this I knew that, if left unchecked, the squirrel could inflict significant damage to our attic overtime.
I borrowed a humane animal trap from my neighbor, and following his advice I baited it with a Reese's Peanut Butter Cup (apparently squirrels are suckers for Reese's Peanut Butter Cups). I left the trap overnight in our attic. The next morning Science Cat seemed to hear something. She would pace back and forth in the room with access to the attic. When I placed the ladder to access the attic, she darted up the ladder and stood at the top looking up, so I had to bring her back down.
I opened the trapdoor to the attic, inspected the trap, and found the varmint. It turned out to be a specimen of Sciurus carolinensis or the eastern grey squirrel. Science Cat took great interest in the squirrel.
My wife and I drove the critter to a nearby forested location and released it into the wild as shown in the video below. There have been no more noises coming from the attic, and I am able to sleep once again just fine.
The photos are property of the author and can only be used with permission.
Forced perspective is a technique that exploits the relationship between distance and size to make large objects appear smaller or vice versa. This technique has been exploited in movies such as The Lord of The Rings franchise to make actors appear smaller (Hobbits) with relation to other actors. The technique is also used by professional photographers to create illusions and also by amateur photographers to create fun pictures. The classic use of the force perspective technique is when people get photographed holding up the leaning tower of Pisa in Italy.
I made a forced perspective photograph of my own while visiting the Rumsey Monument in Shepherdstown, West Virginia. This is a monument to a local inventor, James Rumsey, who in 1787 became the first person in the United States to build and pilot a steamboat. The monument, which is located near the Potomac River where Rumsey made his trek, contains a 75-foot-tall granite column capped with a globe. The column sits atop a 40 square feet concrete base. In the photograph I use forced perspective to make it look like I am wearing the column of the monument on my head!
Leaning tower of Pisa image from flickr by Jeffrey is used here under an Attribution-NoDerivs 2.0 Generic (CC BY-ND 2.0) license. The photographs of the Rumsey monuments belong to the author and can only be used with permission.
The video below features a stela found in the Mayan city of Caracol in Belize, which is exhibited at the Penn Museum in Pennsylvania. Mayans used these stones to mark time. This stela, which shows an image of the ruling king, celebrates a date equivalent to May 10, 613 CE. The stone features an elaborate design that includes the ruler, his attire, and portraits of his ancestors. Besides the anthropological and historical significance of the stone, a thing that caught my attention is how the lines in the figure on the stone were traced.
The creators of the museum exhibit chose an LCD light projector that traces with white lines the contours of the design of the stone when you press a button and them untraces them after several seconds as is shown in the video.
I thought it would be interesting to film the tracing of the design by the projector in slow motion, but I was surprised by the video I obtained which showed the white lines of the stone flickering in a pattern that moved from left to right and that seemed to display occasional flashes of color. When I examined the video frame by frame, I found that the LCD projector did not use white light to create the lines at all. It used an alternating pattern of blue, purple (or red), yellow, and green lines to create the sensation of white lines. This pattern had an apparent left to right movement which maybe has to do with the very fast transition from one color to another..
These types of projectors are quite sophisticated, and if you are interested you can find an explanation of how they work here.
The photographs of the stela can only be used with permission of the author.
While visiting the Lee County Conservation Center in Heron Bend, Lee County, Iowa, I came upon a really cool and fun tool to learn topography. The US Geological Survey calls this tool an “augmented reality sandbox”, and the model at the Lee County Conservation Center was obtained from Idea Fab Labs. Their tool uses a 3D camera, a digital projector, and software that gauges depth and superimposes contour lines on shapes in sandboxes. The tool also allows you to create “rain” by waving your hand on top of the sand so you can see the way watersheds work. I wish I had had access to one of these when I was a kid!
The video below shows a wood stove fan. These fans function with no outside input of electricity. They use the heat gradient between the bottom of the fan in contact with the stove and the top of the fan, which is designed to radiate heat. The bottom to top flow of heat goes through an array of semiconductors. Semiconductors are used in most electronic devices today ranging from smartphones to computers. Semiconductors contain elements such as germanium or compounds such as cadmium selenide combined with specific impurities that alter their physical properties.
In the case of the fan, the elements of the semiconductor sandwiched between the hot and cooler areas of the gradient produce an electric current (Seebeck Effect) that is used to drive a small motor which rotates the blades of the fan. The rotating of the blades propels heat from the stove into the room and helps further cool the top of the fan enhancing the bottom to top heat gradient.
On a recent trip to the University of Tennessee (UT) we learned that robots were delivering food on campus, so we placed an order for Chinese food from the restaurant Panda Express. The robot arrived with our food about 25 minutes after we ordered. When we opened the lid of the robot, it played the song I had chosen (Here Comes the Sun by The Beatles). After retrieving the food and closing the lid, the robot said, “Thank you, go Vols” (the UT team is the “Volunteers”) and drove away.
These self-driving food delivery robots are the creation of the company Starship Technologies. The robots use a combination of machine learning, artificial intelligence, and sensors to cross streets and avoid pedestrians and other obstacles. They can deliver the food during rain, snow, or heat. The company has placed its robots in several university campuses in the U.S. and throughout the world.
Is this the future of food delivery? And what is next? Mail, packages, drones? The future is creeping closer and closer to the present!
Have you ever wondered why cat’s eyes are the way they are? In bright light the pupils of cats look like slits whereas in dim light their pupils look circular. I have documented this phenomenon in the pictures of Science Cat below.
Cats are predators that are biologically designed to hunt at night. The shape of cat’s pupils is an adaptation that reduces the amount of glare during the day and increases the amount of light that enters the eyes during the night. Whereas circular pupils such as those of humans can expand their area 15-fold in going from a fully constricted to a fully dilated shape, those of cats undergo a 135-fold change during this transition. But what allows cats to see better at night is that the density of a type of light receptor in their eyes called “rods” is 6 to 8 times higher than that of a human. Rods permit the detection of very faint light signals. Additionally, cats have a layer of tissue in the back of their retinas called the tapetum lucidum which reflects light back into the light receptors of the eye increasing the amount of light that they can detect. This is why if you use flash photography at night on a cat, like I did with Science Cat below, they look like little demons!
The photographs of Science Cat are property of the author and can only be used with permission.
The art of making music by running a bow against a saw arose in several countries around the world when steel saws became widely available some 300 years ago. In the United States it originated in the Appalachian Mountains and reached a peak in popularity in the vaudeville acts of the 1920s and 1930s but faded towards the second world war. However, the art still endures on today maintained alive by many performers.
The sound produced by a musical saw occurs as a result of the friction exerted by the bow upon the saw which causes the steel surface to vibrate, much in the same way as the string of a guitar vibrates when plucked. These vibrations produce compression waves in the surrounding air which are transmitted to our ears and are perceived as sound.
In a guitar, the pitch of the vibrating string can be adjusted by reducing its effective length, which guitarists do by pressing their fingers to the string. In the musical saw, something similar happens when the performer bends and twists the surface of the saw. This creates bounds that restrict the vibrations and changes their pitch in relation to where the bow is applied. The mathematics of the sounds produced by musical saws is quite complex.
In the video below, former university professor turned street performer, Robert (The Saw Man) Maddox, plays Somewhere My Love (Lara’s theme from the movie Dr. Zhivago) in downtown Knoxville, Tennessee.
In our cultural ethos, rattlesnakes are inextricably linked with the wild west of tumbleweeds, cowboys, horses, sheriffs, and outlaws. These reptiles are indigenous to the Americas and have several notable features. The most distinctive is the rattle at the tip of their tails which they can move 60 or more times per second producing a sound which serves as a warning of their proximity. Rattlesnakes are deaf, but they compensate for this by having a highly developed sense of smell. In fact, the reason why rattlesnakes (and other snakes) constantly stick their tongues in and out of their mouths is to bring scent particles in contact with their smell organs which lie in the roof of the mouth.
Rattlesnakes do not hear sound, rather they have an inner ear that is very sensitive to vibrations in the ground which are transmitted to it by the snake’s muscles and jaw bones. Besides also having very good vision, rattlesnakes have the ability to sense heat thanks to organs located behind each nostril which gives the snakes the ability of heat vision allowing them to hunt in the dark. Rattlesnakes have a venom which they inject through their fangs when they bite much in the same way that a hypodermic needle works. The venom consists of proteins that break down cells and tissues, as well as anticoagulants and neurotoxins that cause circulatory arrest and respiratory paralysis.
The Timber Rattlesnake (Crotalus horridus) featured in the video below was filmed at the Zoo Knoxville in Knoxville, Tennessee.